--- a/toolkit/devtools/server/actors/webconsole.js
+++ b/toolkit/devtools/server/actors/webconsole.js
@@ -806,28 +806,24 @@ WebConsoleActor.prototype =
     let evalInfo = this.evalWithDebugger(input, evalOptions);
     let evalResult = evalInfo.result;
     let helperResult = evalInfo.helperResult;
 
     let result, errorMessage, errorGrip = null;
     if (evalResult) {
       if ("return" in evalResult) {
         result = evalResult.return;
-      }
-      else if ("yield" in evalResult) {
+      } else if ("yield" in evalResult) {
         result = evalResult.yield;
-      }
-      else if ("throw" in evalResult) {
+      } else if ("throw" in evalResult) {
         let error = evalResult.throw;
         errorGrip = this.createValueGrip(error);
-        let errorToString = evalInfo.window
-                            .evalInGlobalWithBindings("ex + ''", {ex: error});
-        if (errorToString && typeof errorToString.return == "string") {
-          errorMessage = errorToString.return;
-        }
+        errorMessage = error && (typeof error === "object")
+          ? error.unsafeDereference().toString()
+          : "" + error;
       }
     }
 
     // If a value is encountered that the debugger server doesn't support yet,
     // the console should remain functional.
     let resultGrip;
     try {
       resultGrip = this.createValueGrip(result);

--- a/toolkit/devtools/webconsole/test/test_jsterm_queryselector.html
+++ b/toolkit/devtools/webconsole/test/test_jsterm_queryselector.html
@@ -18,17 +18,21 @@ let gState;
 function evaluateJS(input) {
   return new Promise((resolve) => gState.client.evaluateJS(input, resolve));
 }
 
 function startTest() {
   removeEventListener("load", startTest);
   attachConsole([], state => {
     gState = state;
-    let tests = [checkQuerySelectorAll, checkQuerySelectorAllNotExist];
+    let tests = [
+      checkQuerySelectorAll,
+      checkQuerySelectorAllNotExist,
+      checkQuerySelectorAllException
+    ];
     runTests(tests, testEnd);
   }, true);
 }
 
 let checkQuerySelectorAll = Task.async(function*() {
   info ("$$ returns an array");
   let response = yield evaluateJS("$$('body')");
   basicResultCheck(response, "$$('body')", {
@@ -49,16 +53,33 @@ let checkQuerySelectorAllNotExist = Task
     class: "Array",
     preview: {
       length: 0
     }
   });
   nextTest();
 });
 
+let checkQuerySelectorAllException = Task.async(function*() {
+  info ("$$ returns an exception if an invalid selector was provided");
+  let response = yield evaluateJS("$$(':foo')");
+  checkObject(response, {
+    input: "$$(':foo')",
+    exceptionMessage: "SyntaxError: An invalid or illegal string was specified",
+    exception: {
+      preview: {
+        kind: "DOMException",
+        name: "SyntaxError",
+        message: "An invalid or illegal string was specified"
+      }
+    }
+  });
+  nextTest();
+});
+
 function basicResultCheck(response, input, output) {
   checkObject(response, {
     from: gState.actor,
     input: input,
     result: output,
   });
   ok(!response.exception, "no eval exception");
   ok(!response.helperResult, "no helper result");

--- a/toolkit/themes/shared/aboutSupport.css
+++ b/toolkit/themes/shared/aboutSupport.css
@@ -29,22 +29,22 @@ button {
 }
 
 table {
   background-color: var(--aboutSupport-table-background);
   color: var(--in-content-text-color);
   font: message-box;
   text-align: start;
   width: 100%;
-  border: 1px solid var(--in-content-table-border-color);
+  border: 1px solid var(--in-content-border-color);
   border-spacing: 0px;
 }
 
 th, td {
-  border: 1px solid var(--in-content-table-border-color);
+  border: 1px solid var(--in-content-border-color);
   padding: 4px;
 }
 
 thead th {
   text-align: center;
 }
 
 th {
@@ -77,17 +77,17 @@ td {
 .pref-value {
   width: 30%;
   white-space: nowrap;
   overflow: hidden;
 }
 
 #action-box {
   background-color: var(--aboutSupport-table-background);
-  border: 1px solid var(--in-content-table-border-color);
+  border: 1px solid var(--in-content-border-color);
   color: var(--in-content-text-color);
   float: right;
   margin-top: 2em;
   margin-bottom: 20px;
   -moz-margin-start: 20px;
   -moz-margin-end: 0;
   padding: 16px;
   width: 30%;