--- a/browser/components/urlbar/UrlbarTokenizer.jsm
+++ b/browser/components/urlbar/UrlbarTokenizer.jsm
@@ -168,17 +168,17 @@ var UrlbarTokenizer = {
    * @param {UrlbarQueryContext} queryContext
    *        The query context object to tokenize
    * @returns {UrlbarQueryContext} the same query context object with a new
    *          tokens property.
    */
   tokenize(queryContext) {
     logger.info("Tokenizing", queryContext);
     let searchString = queryContext.searchString;
-    if (searchString.length == 0) {
+    if (!searchString.trim()) {
       queryContext.tokens = [];
       return queryContext;
     }
 
     let unfiltered = splitString(searchString);
     let tokens = filterTokens(unfiltered);
     queryContext.tokens = tokens;
     return queryContext;

--- a/browser/components/urlbar/UrlbarUtils.jsm
+++ b/browser/components/urlbar/UrlbarUtils.jsm
@@ -216,17 +216,19 @@ var UrlbarUtils = {
    *            ...
    *            [matchIndex_n, matchLength_n]
    *          ].
    *          The array is sorted by match indexes ascending.
    */
   getTokenMatches(tokens, str) {
     return tokens.reduce((matches, token) => {
       let index = 0;
-      while (index >= 0) {
+      // Ideally we should never hit the empty token case, but just in case
+      // the value check protects us from an infinite loop.
+      while (index >= 0 && token.value) {
         index = str.indexOf(token.value, index);
         if (index >= 0) {
           let match = [index, token.value.length];
           let matchesIndex = BinarySearch.insertionIndexOf((a, b) => {
             return a[0] - b[0];
           }, matches, match);
           matches.splice(matchesIndex, 0, match);
           index += token.value.length;

--- a/browser/components/urlbar/UrlbarView.jsm
+++ b/browser/components/urlbar/UrlbarView.jsm
@@ -405,17 +405,17 @@ class UrlbarView {
                                               [result.payload.engine], 1));
         break;
       case UrlbarUtils.RESULT_TYPE.KEYWORD:
         if (result.payload.input.trim() == result.payload.keyword) {
           setAction(bundle.GetStringFromName("visit"));
         }
         break;
       default:
-        if (resultIndex == 0) {
+        if (result.heuristic) {
           setAction(bundle.GetStringFromName("visit"));
         } else {
           setURL();
         }
         break;
     }
     if (action) {
       content.appendChild(action);

--- a/browser/components/urlbar/tests/UrlbarTestUtils.jsm
+++ b/browser/components/urlbar/tests/UrlbarTestUtils.jsm
@@ -370,17 +370,17 @@ class UrlbarAbstraction {
       if (index >= context.results.length) {
         throw new Error("Requested index not found in results");
       }
       let {url, postData} = UrlbarUtils.getUrlFromResult(context.results[index]);
       details.url = url;
       details.postData = postData;
       details.type = context.results[index].type;
       details.heuristic = context.results[index].heuristic;
-      details.autofill = index == 0 && context.results[index].autofill;
+      details.autofill = !!context.results[index].autofill;
       details.image = element.getElementsByClassName("urlbarView-favicon")[0].src;
       details.title = context.results[index].title;
       details.tags = "tags" in context.results[index].payload ?
         context.results[index].payload.tags :
         [];
       let actions = element.getElementsByClassName("urlbarView-action");
       let typeIcon = element.querySelector(".urlbarView-type-icon");
       let typeIconStyle = this.window.getComputedStyle(typeIcon);
@@ -402,22 +402,22 @@ class UrlbarAbstraction {
 
       let style = this.urlbar.controller.getStyleAt(index);
       let action = PlacesUtils.parseActionUrl(this.urlbar.controller.getValueAt(index));
       details.type = getType(style, action);
       details.heuristic = style.includes("heuristic");
       details.autofill = style.includes("autofill");
       details.image = element.getAttribute("image");
       details.title = element.getAttribute("title");
-      details.tags = [...element.getElementsByClassName("ac-tags")].map(e =>
-        e.textContent);
+      details.tags = style.includes("tag") ?
+        [...element.getElementsByClassName("ac-tags")].map(e => e.textContent) : [];
       let typeIconStyle = this.window.getComputedStyle(element._typeIcon);
       details.displayed = {
         title: element._titleText.textContent,
-        action: element._actionText.textContent,
+        action: action ? element._actionText.textContent : "",
         typeIcon: typeIconStyle.listStyleImage,
       };
       if (details.type == UrlbarUtils.RESULT_TYPE.SEARCH) {
         details.searchParams = {
           engine: action.params.engineName,
           keyword: action.params.alias,
           query: action.params.input,
           suggestion: action.params.searchSuggestion,

--- a/browser/components/urlbar/tests/browser/browser.ini
+++ b/browser/components/urlbar/tests/browser/browser.ini
@@ -53,16 +53,17 @@ skip-if = true # Bug 1526222 - Doesn't currently work with QuantumBar
 skip-if = os == 'linux' # Bug 1104755 (Intermittent failure)
 [browser_tabMatchesInAwesomebar.js]
 support-files =
   moz.png
 [browser_urlbar_blanking.js]
 support-files =
   file_blank_but_not_blank.html
 [browser_urlbar_content_opener.js]
+[browser_urlbar_empty_search.js]
 [browser_urlbar_locationchange_urlbar_edit_dos.js]
 support-files =
   file_urlbar_edit_dos.html
 [browser_urlbar_remoteness_switch.js]
 run-if = e10s
 [browser_urlbar_remove_match.js]
 [browser_urlbar_searchsettings.js]
 [browser_urlbar_speculative_connect.js]

new file mode 100644
--- /dev/null
+++ b/browser/components/urlbar/tests/browser/browser_urlbar_empty_search.js
@@ -0,0 +1,47 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+// This test ensures that a search for "empty" strings doesn't break the urlbar.
+
+add_task(async function test_setup() {
+  await PlacesTestUtils.addVisits([
+    {
+      uri: `http://one.mozilla.org/`,
+      transition: PlacesUtils.history.TRANSITIONS.TYPED,
+    },
+    {
+      uri: `http://two.mozilla.org/`,
+      transition: PlacesUtils.history.TRANSITIONS.TYPED,
+    },
+  ]);
+  registerCleanupFunction(PlacesUtils.history.clear);
+});
+
+add_task(async function test_empty() {
+  info("Test searching for nothing");
+  await promiseAutocompleteResultPopup("", window, true);
+  // The first search collects the results, the following ones check results
+  // are the same.
+  let results = [{}]; // Add a fake first result, to account for heuristic.
+  for (let i = 0; i < await UrlbarTestUtils.getResultCount(window); ++i) {
+    results.push(await UrlbarTestUtils.getDetailsOfResultAt(window, i));
+  }
+
+  for (let str of [" ", "  "]) {
+    info(`Test searching for "${str}"`);
+    await promiseAutocompleteResultPopup(str, window, true);
+    // Skip the heuristic result.
+    Assert.ok((await UrlbarTestUtils.getDetailsOfResultAt(window, 0)).heuristic,
+              "The first result is heuristic");
+    let length = await UrlbarTestUtils.getResultCount(window);
+    Assert.equal(length, results.length, "Comparing results count");
+    for (let i = 1; i < length; ++i) {
+      Assert.deepEqual(await UrlbarTestUtils.getDetailsOfResultAt(window, i),
+                        results[i],
+                       `Comparing result at index ${i}`);
+    }
+  }
+});

--- a/browser/components/urlbar/tests/legacy/browser.ini
+++ b/browser/components/urlbar/tests/legacy/browser.ini
@@ -95,16 +95,17 @@ subsuite = clipboard
 support-files =
   ../browser/authenticate.sjs
 [../browser/browser_urlbarCutting.js]
 [../browser/browser_urlbarDecode.js]
 [../browser/browser_urlbar_blanking.js]
 support-files =
   ../browser/file_blank_but_not_blank.html
 [../browser/browser_urlbar_content_opener.js]
+[../browser/browser_urlbar_empty_search.js]
 [../browser/browser_urlbar_locationchange_urlbar_edit_dos.js]
 support-files =
   ../browser/file_urlbar_edit_dos.html
 [../browser/browser_urlbarDelete.js]
 [../browser/browser_urlbarEnter.js]
 [../browser/browser_urlbarEnterAfterMouseOver.js]
 skip-if = os == "linux" # Bug 1073339 - Investigate autocomplete test unreliability on Linux/e10s
 [../browser/browser_urlbar_whereToOpen.js]

--- a/browser/components/urlbar/tests/unit/test_tokenizer.js
+++ b/browser/components/urlbar/tests/unit/test_tokenizer.js
@@ -2,16 +2,20 @@
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 add_task(async function test_tokenizer() {
   let testContexts = [
     { desc: "Empty string",
       searchString: "",
       expectedTokens: [],
     },
+    { desc: "Spaces string",
+      searchString: "      ",
+      expectedTokens: [],
+    },
     { desc: "Single word string",
       searchString: "test",
       expectedTokens: [
         { value: "test", type: UrlbarTokenizer.TYPE.POSSIBLE_ORIGIN },
       ],
     },
     { desc: "Multi word string with mixed whitespace types",
       searchString: " test1 test2\u1680test3\u2004test4\u1680",