--- a/browser/extensions/pdfjs/README.mozilla
+++ b/browser/extensions/pdfjs/README.mozilla
@@ -1,5 +1,5 @@
 This is the PDF.js project output, https://github.com/mozilla/pdf.js
 
-Current extension version is: 2.4.326
+Current extension version is: 2.4.349
 
-Taken from upstream commit: d6754d1e
+Taken from upstream commit: dced0a38

--- a/browser/extensions/pdfjs/content/build/pdf.js
+++ b/browser/extensions/pdfjs/content/build/pdf.js
@@ -118,18 +118,18 @@ return /******/ (function(modules) { // 
 /************************************************************************/
 /******/ ([
 /* 0 */
 /***/ (function(module, exports, __w_pdfjs_require__) {
 
 "use strict";
 
 
-var pdfjsVersion = '2.4.326';
-var pdfjsBuild = 'd6754d1e';
+var pdfjsVersion = '2.4.349';
+var pdfjsBuild = 'dced0a38';
 
 var pdfjsSharedUtil = __w_pdfjs_require__(1);
 
 var pdfjsDisplayAPI = __w_pdfjs_require__(3);
 
 var pdfjsDisplayTextLayer = __w_pdfjs_require__(16);
 
 var pdfjsDisplayAnnotationLayer = __w_pdfjs_require__(17);
@@ -1200,17 +1200,17 @@ function _fetchDocument(worker, source, 
   if (pdfDataRangeTransport) {
     source.length = pdfDataRangeTransport.length;
     source.initialData = pdfDataRangeTransport.initialData;
     source.progressiveDone = pdfDataRangeTransport.progressiveDone;
   }
 
   return worker.messageHandler.sendWithPromise("GetDocRequest", {
     docId,
-    apiVersion: '2.4.326',
+    apiVersion: '2.4.349',
     source: {
       data: source.data,
       url: source.url,
       password: source.password,
       disableAutoFetch: source.disableAutoFetch,
       rangeChunkSize: source.rangeChunkSize,
       length: source.length
     },
@@ -1423,17 +1423,17 @@ class PDFDocumentProxy {
     return this._transport.downloadInfoCapability.promise;
   }
 
   getStats() {
     return this._transport.getStats();
   }
 
   cleanup() {
-    this._transport.startCleanup();
+    return this._transport.startCleanup();
   }
 
   destroy() {
     return this.loadingTask.destroy();
   }
 
   get loadingParams() {
     return this._transport.loadingParams;
@@ -1754,39 +1754,39 @@ class PDFPageProxy {
     this.objs.clear();
     this.annotationsPromise = null;
     this.pendingCleanup = false;
     return Promise.all(waitOn);
   }
 
   cleanup(resetStats = false) {
     this.pendingCleanup = true;
-
-    this._tryCleanup(resetStats);
+    return this._tryCleanup(resetStats);
   }
 
   _tryCleanup(resetStats = false) {
     if (!this.pendingCleanup || Object.keys(this.intentStates).some(intent => {
       const intentState = this.intentStates[intent];
       return intentState.renderTasks.length !== 0 || !intentState.operatorList.lastChunk;
     })) {
-      return;
+      return false;
     }
 
     Object.keys(this.intentStates).forEach(intent => {
       delete this.intentStates[intent];
     });
     this.objs.clear();
     this.annotationsPromise = null;
 
     if (resetStats && this._stats) {
       this._stats = new _display_utils.StatTimer();
     }
 
     this.pendingCleanup = false;
+    return true;
   }
 
   _startRenderPage(transparency, intent) {
     const intentState = this.intentStates[intent];
 
     if (!intentState) {
       return;
     }
@@ -2869,22 +2869,26 @@ class WorkerTransport {
     });
   }
 
   getStats() {
     return this.messageHandler.sendWithPromise("GetStats", null);
   }
 
   startCleanup() {
-    this.messageHandler.sendWithPromise("Cleanup", null).then(() => {
+    return this.messageHandler.sendWithPromise("Cleanup", null).then(() => {
       for (let i = 0, ii = this.pageCache.length; i < ii; i++) {
         const page = this.pageCache[i];
 
         if (page) {
-          page.cleanup();
+          const cleanupSuccessful = page.cleanup();
+
+          if (!cleanupSuccessful) {
+            throw new Error(`startCleanup: Page ${i + 1} is currently rendering.`);
+          }
         }
       }
 
       this.commonObjs.clear();
       this.fontLoader.clear();
     });
   }
 
@@ -3143,19 +3147,19 @@ const InternalRenderTask = function Inte
       }
     }
 
   }
 
   return InternalRenderTask;
 }();
 
-const version = '2.4.326';
+const version = '2.4.349';
 exports.version = version;
-const build = 'd6754d1e';
+const build = 'dced0a38';
 exports.build = build;
 
 /***/ }),
 /* 4 */
 /***/ (function(module, exports, __w_pdfjs_require__) {
 
 "use strict";
 

--- a/browser/extensions/pdfjs/content/build/pdf.worker.js
+++ b/browser/extensions/pdfjs/content/build/pdf.worker.js
@@ -118,18 +118,18 @@ return /******/ (function(modules) { // 
 /************************************************************************/
 /******/ ([
 /* 0 */
 /***/ (function(module, exports, __w_pdfjs_require__) {
 
 "use strict";
 
 
-const pdfjsVersion = '2.4.326';
-const pdfjsBuild = 'd6754d1e';
+const pdfjsVersion = '2.4.349';
+const pdfjsBuild = 'dced0a38';
 
 const pdfjsCoreWorker = __w_pdfjs_require__(1);
 
 exports.WorkerMessageHandler = pdfjsCoreWorker.WorkerMessageHandler;
 
 /***/ }),
 /* 1 */
 /***/ (function(module, exports, __w_pdfjs_require__) {
@@ -218,17 +218,17 @@ var WorkerMessageHandler = {
 
   createDocumentHandler(docParams, port) {
     var pdfManager;
     var terminated = false;
     var cancelXHRs = null;
     var WorkerTasks = [];
     const verbosity = (0, _util.getVerbosityLevel)();
     const apiVersion = docParams.apiVersion;
-    const workerVersion = '2.4.326';
+    const workerVersion = '2.4.349';
 
     if (apiVersion !== workerVersion) {
       throw new Error(`The API version "${apiVersion}" does not match ` + `the Worker version "${workerVersion}".`);
     }
 
     var docId = docParams.docId;
     var docBaseUrl = docParams.docBaseUrl;
     var workerHandlerName = docParams.docId + "_worker";
@@ -3092,16 +3092,17 @@ class Page {
 }
 
 exports.Page = Page;
 const PDF_HEADER_SIGNATURE = new Uint8Array([0x25, 0x50, 0x44, 0x46, 0x2d]);
 const STARTXREF_SIGNATURE = new Uint8Array([0x73, 0x74, 0x61, 0x72, 0x74, 0x78, 0x72, 0x65, 0x66]);
 const ENDOBJ_SIGNATURE = new Uint8Array([0x65, 0x6e, 0x64, 0x6f, 0x62, 0x6a]);
 const FINGERPRINT_FIRST_BYTES = 1024;
 const EMPTY_FINGERPRINT = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00";
+const PDF_HEADER_VERSION_REGEXP = /^[1-9]\.[0-9]$/;
 
 function find(stream, signature, limit = 1024, backwards = false) {
   const signatureLength = signature.length;
   const scanBytes = stream.peekBytes(limit);
   const scanLength = scanBytes.length - signatureLength;
 
   if (scanLength <= 0) {
     return false;
@@ -3333,18 +3334,25 @@ class PDFDocument {
       Subject: _util.isString,
       Keywords: _util.isString,
       Creator: _util.isString,
       Producer: _util.isString,
       CreationDate: _util.isString,
       ModDate: _util.isString,
       Trapped: _primitives.isName
     };
+    let version = this.pdfFormatVersion;
+
+    if (typeof version !== "string" || !PDF_HEADER_VERSION_REGEXP.test(version)) {
+      (0, _util.warn)(`Invalid PDF header version number: ${version}`);
+      version = null;
+    }
+
     const docInfo = {
-      PDFFormatVersion: this.pdfFormatVersion,
+      PDFFormatVersion: version,
       IsLinearized: !!this.linearization,
       IsAcroFormPresent: !!this.acroForm,
       IsXFAPresent: !!this.xfa,
       IsCollectionPresent: !!this.collection
     };
     let infoDict;
 
     try {
@@ -12898,28 +12906,33 @@ var JpegImage = function JpegImageClosur
       var index;
       var offset = 0;
       var output;
       var numComponents = this.components.length;
       var dataLength = width * height * numComponents;
       var data = new Uint8ClampedArray(dataLength);
       var xScaleBlockOffset = new Uint32Array(width);
       var mask3LSB = 0xfffffff8;
+      let lastComponentScaleX;
 
       for (i = 0; i < numComponents; i++) {
         component = this.components[i];
         componentScaleX = component.scaleX * scaleX;
         componentScaleY = component.scaleY * scaleY;
         offset = i;
         output = component.output;
         blocksPerScanline = component.blocksPerLine + 1 << 3;
 
-        for (x = 0; x < width; x++) {
-          j = 0 | x * componentScaleX;
-          xScaleBlockOffset[x] = (j & mask3LSB) << 3 | j & 7;
+        if (componentScaleX !== lastComponentScaleX) {
+          for (x = 0; x < width; x++) {
+            j = 0 | x * componentScaleX;
+            xScaleBlockOffset[x] = (j & mask3LSB) << 3 | j & 7;
+          }
+
+          lastComponentScaleX = componentScaleX;
         }
 
         for (y = 0; y < height; y++) {
           j = 0 | y * componentScaleY;
           index = blocksPerScanline * (j & mask3LSB) | (j & 7) << 3;
 
           for (x = 0; x < width; x++) {
             data[offset] = output[index + xScaleBlockOffset[x]];
@@ -13007,26 +13020,25 @@ var JpegImage = function JpegImageClosur
         data[i + 2] = 481.816 - Y - 1.772 * Cb;
       }
 
       return data;
     },
     _convertCmykToRgb: function convertCmykToRgb(data) {
       var c, m, y, k;
       var offset = 0;
-      var scale = 1 / 255;
 
       for (var i = 0, length = data.length; i < length; i += 4) {
-        c = data[i] * scale;
-        m = data[i + 1] * scale;
-        y = data[i + 2] * scale;
-        k = data[i + 3] * scale;
-        data[offset++] = 255 + c * (-4.387332384609988 * c + 54.48615194189176 * m + 18.82290502165302 * y + 212.25662451639585 * k - 285.2331026137004) + m * (1.7149763477362134 * m - 5.6096736904047315 * y - 17.873870861415444 * k - 5.497006427196366) + y * (-2.5217340131683033 * y - 21.248923337353073 * k + 17.5119270841813) - k * (21.86122147463605 * k + 189.48180835922747);
-        data[offset++] = 255 + c * (8.841041422036149 * c + 60.118027045597366 * m + 6.871425592049007 * y + 31.159100130055922 * k - 79.2970844816548) + m * (-15.310361306967817 * m + 17.575251261109482 * y + 131.35250912493976 * k - 190.9453302588951) + y * (4.444339102852739 * y + 9.8632861493405 * k - 24.86741582555878) - k * (20.737325471181034 * k + 187.80453709719578);
-        data[offset++] = 255 + c * (0.8842522430003296 * c + 8.078677503112928 * m + 30.89978309703729 * y - 0.23883238689178934 * k - 14.183576799673286) + m * (10.49593273432072 * m + 63.02378494754052 * y + 50.606957656360734 * k - 112.23884253719248) + y * (0.03296041114873217 * y + 115.60384449646641 * k - 193.58209356861505) - k * (22.33816807309886 * k + 180.12613974708367);
+        c = data[i];
+        m = data[i + 1];
+        y = data[i + 2];
+        k = data[i + 3];
+        data[offset++] = 255 + c * (-0.00006747147073602441 * c + 0.0008379262121013727 * m + 0.0002894718188643294 * y + 0.003264231057537806 * k - 1.1185611867203937) + m * (0.000026374107616089405 * m - 0.00008626949158638572 * y - 0.0002748769067499491 * k - 0.02155688794978967) + y * (-0.00003878099212869363 * y - 0.0003267808279485286 * k + 0.0686742238595345) - k * (0.0003361971776183937 * k + 0.7430659151342254);
+        data[offset++] = 255 + c * (0.00013596372813588848 * c + 0.000924537132573585 * m + 0.00010567359618683593 * y + 0.0004791864687436512 * k - 0.3109689587515875) + m * (-0.00023545346108370344 * m + 0.0002702845253534714 * y + 0.0020200308977307156 * k - 0.7488052167015494) + y * (0.00006834815998235662 * y + 0.00015168452363460973 * k - 0.09751927774728933) - k * (0.00031891311758832814 * k + 0.7364883807733168);
+        data[offset++] = 255 + c * (0.000013598650411385307 * c + 0.00012423956175490851 * m + 0.0004751985097583589 * y - 0.0000036729317476630422 * k - 0.05562186980264034) + m * (0.00016141380598724676 * m + 0.0009692239130725186 * y + 0.0007782692450036253 * k - 0.44015232367526463) + y * (5.068882914068769e-7 * y + 0.0017778369011375071 * k - 0.7591454649749609) - k * (0.0003435319965105553 * k + 0.7063770186160144);
       }
 
       return data.subarray(0, offset);
     },
 
     getData({
       width,
       height,
@@ -22114,16 +22126,30 @@ var PartialEvaluator = function PartialE
               k += 2;
               var w2 = token.charCodeAt(k) << 8 | token.charCodeAt(k + 1);
               str.push(((w1 & 0x3ff) << 10) + (w2 & 0x3ff) + 0x10000);
             }
 
             map[charCode] = String.fromCodePoint.apply(String, str);
           });
           return new _fonts.ToUnicodeMap(map);
+        }, reason => {
+          if (reason instanceof _util.AbortException) {
+            return null;
+          }
+
+          if (this.options.ignoreErrors) {
+            this.handler.send("UnsupportedFeature", {
+              featureId: _util.UNSUPPORTED_FEATURES.font
+            });
+            (0, _util.warn)(`readToUnicode - ignoring ToUnicode data: "${reason}".`);
+            return null;
+          }
+
+          throw reason;
         });
       }
 
       return Promise.resolve(null);
     },
 
     readCidToGidMap(glyphsData, toUnicode) {
       var result = [];
@@ -22404,16 +22430,18 @@ var PartialEvaluator = function PartialE
     translateFont: function PartialEvaluator_translateFont(preEvaluatedFont) {
       var baseDict = preEvaluatedFont.baseDict;
       var dict = preEvaluatedFont.dict;
       var composite = preEvaluatedFont.composite;
       var descriptor = preEvaluatedFont.descriptor;
       var type = preEvaluatedFont.type;
       var maxCharIndex = composite ? 0xffff : 0xff;
       var properties;
+      const firstChar = dict.get("FirstChar") || 0;
+      const lastChar = dict.get("LastChar") || maxCharIndex;
 
       if (!descriptor) {
         if (type === "Type3") {
           descriptor = new _primitives.Dict(null);
           descriptor.set("FontName", _primitives.Name.get(type));
           descriptor.set("FontBBox", dict.getArray("FontBBox"));
         } else {
           var baseFontName = dict.get("BaseFont");
@@ -22427,28 +22455,39 @@ var PartialEvaluator = function PartialE
           var fontNameWoStyle = baseFontName.split("-")[0];
           var flags = (this.isSerifFont(fontNameWoStyle) ? _fonts.FontFlags.Serif : 0) | (metrics.monospace ? _fonts.FontFlags.FixedPitch : 0) | ((0, _standard_fonts.getSymbolsFonts)()[fontNameWoStyle] ? _fonts.FontFlags.Symbolic : _fonts.FontFlags.Nonsymbolic);
           properties = {
             type,
             name: baseFontName,
             widths: metrics.widths,
             defaultWidth: metrics.defaultWidth,
             flags,
-            firstChar: 0,
-            lastChar: maxCharIndex
+            firstChar,
+            lastChar
           };
+          const widths = dict.get("Widths");
           return this.extractDataStructures(dict, dict, properties).then(properties => {
-            properties.widths = this.buildCharCodeToWidth(metrics.widths, properties);
+            if (widths) {
+              const glyphWidths = [];
+              let j = firstChar;
+
+              for (let i = 0, ii = widths.length; i < ii; i++) {
+                glyphWidths[j++] = this.xref.fetchIfRef(widths[i]);
+              }
+
+              properties.widths = glyphWidths;
+            } else {
+              properties.widths = this.buildCharCodeToWidth(metrics.widths, properties);
+            }
+
             return new _fonts.Font(baseFontName, null, properties);
           });
         }
       }
 
-      var firstChar = dict.get("FirstChar") || 0;
-      var lastChar = dict.get("LastChar") || maxCharIndex;
       var fontName = descriptor.get("FontName");
       var baseFont = dict.get("BaseFont");
 
       if ((0, _util.isString)(fontName)) {
         fontName = _primitives.Name.get(fontName);
       }
 
       if ((0, _util.isString)(baseFont)) {
@@ -24175,17 +24214,17 @@ var CMapFactory = function CMapFactoryCl
         return parseCMap(cMap, lexer, fetchBuiltInCMap, null);
       }
 
       return Promise.reject(new Error("TODO: Only BINARY/NONE CMap compression is currently supported."));
     });
   }
 
   return {
-    create(params) {
+    async create(params) {
       var encoding = params.encoding;
       var fetchBuiltInCMap = params.fetchBuiltInCMap;
       var useCMap = params.useCMap;
 
       if ((0, _primitives.isName)(encoding)) {
         return createBuiltInCMap(encoding.name, fetchBuiltInCMap);
       } else if ((0, _primitives.isStream)(encoding)) {
         var cMap = new CMap();
@@ -24194,17 +24233,17 @@ var CMapFactory = function CMapFactoryCl
           if (parsedCMap.isIdentityCMap) {
             return createBuiltInCMap(parsedCMap.name, fetchBuiltInCMap);
           }
 
           return parsedCMap;
         });
       }
 
-      return Promise.reject(new Error("Encoding required."));
+      throw new Error("Encoding required.");
     }
 
   };
 }();
 
 exports.CMapFactory = CMapFactory;
 
 /***/ }),
@@ -25218,17 +25257,17 @@ var Font = function FontClosure() {
       return data;
     },
     fallbackToSystemFont: function Font_fallbackToSystemFont() {
       this.missingFile = true;
       var charCode, unicode;
       var name = this.name;
       var type = this.type;
       var subtype = this.subtype;
-      var fontName = name.replace(/[,_]/g, "-");
+      let fontName = name.replace(/[,_]/g, "-").replace(/\s/g, "");
       var stdFontMap = (0, _standard_fonts.getStdFontMap)(),
           nonStdFontMap = (0, _standard_fonts.getNonStdFontMap)();
       var isStandardFont = !!stdFontMap[fontName] || !!(nonStdFontMap[fontName] && stdFontMap[nonStdFontMap[fontName]]);
       fontName = stdFontMap[fontName] || nonStdFontMap[fontName] || fontName;
       this.bold = fontName.search(/bold/gi) !== -1;
       this.italic = fontName.search(/oblique/gi) !== -1 || fontName.search(/italic/gi) !== -1;
       this.black = name.search(/Black/g) !== -1;
       this.remeasure = Object.keys(this.widths).length > 0;
@@ -26856,16 +26895,22 @@ var Font = function FontClosure() {
       if (typeof unicode === "number") {
         unicode = String.fromCharCode(unicode);
       }
 
       var isInFont = charcode in this.toFontChar;
       fontCharCode = this.toFontChar[charcode] || charcode;
 
       if (this.missingFile) {
+        const glyphName = this.differences[charcode] || this.defaultEncoding[charcode];
+
+        if ((glyphName === ".notdef" || glyphName === "") && this.type === "Type1") {
+          fontCharCode = 0x20;
+        }
+
         fontCharCode = (0, _unicode.mapSpecialUnicodeValues)(fontCharCode);
       }
 
       if (this.isType3Font) {
         operatorListId = fontCharCode;
       }
 
       var accent = null;

--- a/browser/extensions/pdfjs/content/web/debugger.js
+++ b/browser/extensions/pdfjs/content/web/debugger.js
@@ -62,17 +62,16 @@ var FontInspector = (function FontInspec
   return {
     // Properties/functions needed by PDFBug.
     id: "FontInspector",
     name: "Font Inspector",
     panel: null,
     manager: null,
     init: function init(pdfjsLib) {
       var panel = this.panel;
-      panel.setAttribute("style", "padding: 5px;");
       var tmp = document.createElement("button");
       tmp.addEventListener("click", resetSelection);
       tmp.textContent = "Refresh";
       panel.appendChild(tmp);
 
       fonts = document.createElement("div");
       panel.appendChild(fonts);
     },
@@ -173,17 +172,16 @@ var StepperManager = (function StepperMa
   return {
     // Properties/functions needed by PDFBug.
     id: "Stepper",
     name: "Stepper",
     panel: null,
     manager: null,
     init: function init(pdfjsLib) {
       var self = this;
-      this.panel.setAttribute("style", "padding: 5px;");
       stepperControls = document.createElement("div");
       stepperChooser = document.createElement("select");
       stepperChooser.addEventListener("change", function(event) {
         self.selectStepper(this.value);
       });
       stepperControls.appendChild(stepperChooser);
       stepperDiv = document.createElement("div");
       this.panel.appendChild(stepperControls);
@@ -463,19 +461,17 @@ var Stats = (function Stats() {
     return false;
   }
   return {
     // Properties/functions needed by PDFBug.
     id: "Stats",
     name: "Stats",
     panel: null,
     manager: null,
-    init(pdfjsLib) {
-      this.panel.setAttribute("style", "padding: 5px;");
-    },
+    init(pdfjsLib) {},
     enabled: false,
     active: false,
     // Stats specific functions.
     add(pageNumber, stat) {
       if (!stat) {
         return;
       }
       var statsIndex = getStatIndex(pageNumber);

--- a/browser/extensions/pdfjs/content/web/viewer.css
+++ b/browser/extensions/pdfjs/content/web/viewer.css
@@ -376,16 +376,18 @@
 
 .pdfPresentationMode:fullscreen .pdfViewer .page {
   margin-bottom: 100%;
   border: 0;
 }
 
 :root {
   --sidebar-width: 200px;
+  --sidebar-transition-duration: 200ms;
+  --sidebar-transition-timing-function: ease;
 }
 
 * {
   padding: 0;
   margin: 0;
 }
 
 html {
@@ -446,34 +448,30 @@ select {
   height: 100%;
   position: relative;
 }
 
 #sidebarContainer {
   position: absolute;
   top: 32px;
   bottom: 0;
-  width: 200px; /* Here, and elsewhere below, keep the constant value for compatibility
-                   with older browsers that lack support for CSS variables. */
   width: var(--sidebar-width);
   visibility: hidden;
   z-index: 100;
   border-top: 1px solid rgba(51, 51, 51, 1);
-  transition-duration: 200ms;
-  transition-timing-function: ease;
+  transition-duration: var(--sidebar-transition-duration);
+  transition-timing-function: var(--sidebar-transition-timing-function);
 }
 html[dir='ltr'] #sidebarContainer {
   transition-property: left;
-  left: -200px;
-  left: calc(-1 * var(--sidebar-width));
+  left: calc(0px - var(--sidebar-width));
 }
 html[dir='rtl'] #sidebarContainer {
   transition-property: right;
-  right: -200px;
-  right: calc(-1 * var(--sidebar-width));
+  right: calc(0px - var(--sidebar-width));
 }
 
 .loadingInProgress #sidebarContainer {
   top: 36px;
 }
 
 #outerContainer.sidebarResizing #sidebarContainer {
   /* Improve responsiveness and avoid visual glitches when the sidebar is resized. */
@@ -524,39 +522,37 @@ html[dir='rtl'] #sidebarContent {
   position: absolute;
   top: 32px;
   right: 0;
   bottom: 0;
   left: 0;
   outline: none;
 }
 #viewerContainer:not(.pdfPresentationMode) {
-  transition-duration: 200ms;
-  transition-timing-function: ease;
+  transition-duration: var(--sidebar-transition-duration);
+  transition-timing-function: var(--sidebar-transition-timing-function);
 }
 html[dir='ltr'] #viewerContainer {
   box-shadow: inset 1px 0 0 rgba(255, 255, 255, 0.05);
 }
 html[dir='rtl'] #viewerContainer {
   box-shadow: inset -1px 0 0 rgba(255, 255, 255, 0.05);
 }
 
 #outerContainer.sidebarResizing #viewerContainer {
   /* Improve responsiveness and avoid visual glitches when the sidebar is resized. */
   transition-duration: 0s;
 }
 
 html[dir='ltr'] #outerContainer.sidebarOpen #viewerContainer:not(.pdfPresentationMode) {
   transition-property: left;
-  left: 200px;
   left: var(--sidebar-width);
 }
 html[dir='rtl'] #outerContainer.sidebarOpen #viewerContainer:not(.pdfPresentationMode) {
   transition-property: right;
-  right: 200px;
   right: var(--sidebar-width);
 }
 
 .toolbar {
   position: relative;
   left: 0;
   right: 0;
   z-index: 9999;
@@ -1044,31 +1040,31 @@ html[dir='rtl'] .dropdownToolbarButton {
   background-color: rgba(0, 0, 0, 0.4);
   border-color: rgba(0, 0, 0, 0.4) rgba(0, 0, 0, 0.5) rgba(0, 0, 0, 0.55);
   box-shadow: 0 1px 1px rgba(0, 0, 0, 0.2) inset,
               0 0 1px rgba(0, 0, 0, 0.3) inset,
               0 1px 0 rgba(255, 255, 255, 0.05);
 }
 
 .dropdownToolbarButton {
-  width: 120px;
-  max-width: 120px;
+  width: 140px;
   padding: 0;
   overflow: hidden;
   background: url(images/toolbarButton-menuArrows.png) no-repeat;
 }
 html[dir='ltr'] .dropdownToolbarButton {
   background-position: 95%;
 }
 html[dir='rtl'] .dropdownToolbarButton {
   background-position: 5%;
 }
 
 .dropdownToolbarButton > select {
-  min-width: 140px;
+  width: 162px;
+  height: 23px;
   font-size: 12px;
   color: rgba(242, 242, 242, 1);
   margin: 0;
   padding: 3px 2px 2px;
   border: none;
   background: rgba(0,0,0,0); /* Opera does not support 'transparent' <select> background */
 }
 
@@ -1817,16 +1813,19 @@ html[dir='rtl'] #documentPropertiesOverl
 #PDFBug .panels {
   bottom: 0;
   left: 0;
   overflow: auto;
   position: absolute;
   right: 0;
   top: 27px;
 }
+#PDFBug .panels > div {
+  padding: 5px;
+}
 #PDFBug button.active {
   font-weight: bold;
 }
 .debuggerShowText {
   background: none repeat scroll 0 0 rgba(255, 255, 0, 1);
   color: rgba(0, 0, 255, 1);
 }
 .debuggerHideText:hover {

--- a/browser/extensions/pdfjs/content/web/viewer.js
+++ b/browser/extensions/pdfjs/content/web/viewer.js
@@ -3123,17 +3123,17 @@ class ProgressBar {
     if (!viewer) {
       return;
     }
 
     const container = viewer.parentNode;
     const scrollbarWidth = container.offsetWidth - viewer.offsetWidth;
 
     if (scrollbarWidth > 0) {
-      this.bar.setAttribute("style", "width: calc(100% - " + scrollbarWidth + "px);");
+      this.bar.style.width = `calc(100% - ${scrollbarWidth}px)`;
     }
   }
 
   hide() {
     if (!this.visible) {
       return;
     }
 
@@ -6954,28 +6954,22 @@ class PDFOutlineViewer {
       return false;
     };
   }
 
   _setStyles(element, {
     bold,
     italic
   }) {
-    let styleStr = "";
-
     if (bold) {
-      styleStr += "font-weight: bold;";
+      element.style.fontWeight = "bold";
     }
 
     if (italic) {
-      styleStr += "font-style: italic;";
-    }
-
-    if (styleStr) {
-      element.setAttribute("style", styleStr);
+      element.style.fontStyle = "italic";
     }
   }
 
   _addToggleButton(div, {
     count,
     items
   }) {
     const toggler = document.createElement("div");
@@ -10804,17 +10798,17 @@ class SecondaryToolbar {
     }
 
     this.containerHeight = this.mainContainer.clientHeight;
 
     if (this.containerHeight === this.previousContainerHeight) {
       return;
     }
 
-    this.toolbarButtonContainer.setAttribute("style", "max-height: " + (this.containerHeight - _ui_utils.SCROLLBAR_PADDING) + "px;");
+    this.toolbarButtonContainer.style.maxHeight = `${this.containerHeight - _ui_utils.SCROLLBAR_PADDING}px`;
     this.previousContainerHeight = this.containerHeight;
   }
 
 }
 
 exports.SecondaryToolbar = SecondaryToolbar;
 
 /***/ }),
@@ -10948,18 +10942,18 @@ exports.PDFSinglePageViewer = PDFSingleP
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
 exports.Toolbar = void 0;
 
 var _ui_utils = __webpack_require__(2);
 
 const PAGE_NUMBER_LOADING_INDICATOR = "visiblePageIsLoading";
-const SCALE_SELECT_CONTAINER_PADDING = 8;
-const SCALE_SELECT_PADDING = 22;
+const SCALE_SELECT_CONTAINER_WIDTH = 140;
+const SCALE_SELECT_WIDTH = 162;
 
 class Toolbar {
   constructor(options, eventBus, l10n = _ui_utils.NullL10n) {
     this.toolbar = options.container;
     this.eventBus = eventBus;
     this.l10n = l10n;
     this.buttons = [{
       element: options.previous,
@@ -11156,32 +11150,56 @@ class Toolbar {
     });
   }
 
   updateLoadingIndicatorState(loading = false) {
     const pageNumberInput = this.items.pageNumber;
     pageNumberInput.classList.toggle(PAGE_NUMBER_LOADING_INDICATOR, loading);
   }
 
-  _adjustScaleWidth() {
-    const container = this.items.scaleSelectContainer;
-    const select = this.items.scaleSelect;
-
-    _ui_utils.animationStarted.then(function () {
-      if (container.clientWidth === 0) {
-        container.setAttribute("style", "display: inherit;");
-      }
-
-      if (container.clientWidth > 0) {
-        select.setAttribute("style", "min-width: inherit;");
-        const width = select.clientWidth + SCALE_SELECT_CONTAINER_PADDING;
-        select.setAttribute("style", `min-width: ${width + SCALE_SELECT_PADDING}px;`);
-        container.setAttribute("style", `min-width: ${width}px; max-width: ${width}px;`);
-      }
-    });
+  async _adjustScaleWidth() {
+    const {
+      items,
+      l10n
+    } = this;
+    const predefinedValuesPromise = Promise.all([l10n.get("page_scale_auto", null, "Automatic Zoom"), l10n.get("page_scale_actual", null, "Actual Size"), l10n.get("page_scale_fit", null, "Page Fit"), l10n.get("page_scale_width", null, "Page Width")]);
+    let canvas = document.createElement("canvas");
+    canvas.mozOpaque = true;
+    let ctx = canvas.getContext("2d", {
+      alpha: false
+    });
+    await _ui_utils.animationStarted;
+    const {
+      fontSize,
+      fontFamily
+    } = getComputedStyle(items.scaleSelect);
+    ctx.font = `${fontSize} ${fontFamily}`;
+    let maxWidth = 0;
+
+    for (const predefinedValue of await predefinedValuesPromise) {
+      const {
+        width
+      } = ctx.measureText(predefinedValue);
+
+      if (width > maxWidth) {
+        maxWidth = width;
+      }
+    }
+
+    const overflow = SCALE_SELECT_WIDTH - SCALE_SELECT_CONTAINER_WIDTH;
+    maxWidth += 1.5 * overflow;
+
+    if (maxWidth > SCALE_SELECT_CONTAINER_WIDTH) {
+      items.scaleSelect.style.width = `${maxWidth + overflow}px`;
+      items.scaleSelectContainer.style.width = `${maxWidth}px`;
+    }
+
+    canvas.width = 0;
+    canvas.height = 0;
+    canvas = ctx = null;
   }
 
 }
 
 exports.Toolbar = Toolbar;
 
 /***/ }),
 /* 32 */

--- a/browser/extensions/pdfjs/moz.yaml
+++ b/browser/extensions/pdfjs/moz.yaml
@@ -15,15 +15,15 @@ origin:
   description: Portable Document Format (PDF) viewer that is built with HTML5
 
   # Full URL for the package's homepage/etc
   # Usually different from repository url
   url: https://github.com/mozilla/pdf.js
 
   # Human-readable identifier for this version/release
   # Generally "version NNN", "tag SSS", "bookmark SSS"
-  release: version 2.4.326
+  release: version 2.4.349
 
   # The package's license, where possible using the mnemonic from
   # https://spdx.org/licenses/
   # Multiple licenses can be specified (as a YAML list)
   # A "LICENSE" file must exist containing the full license text
   license: Apache-2.0