diff --git a/toolkit/content/tests/chrome/test_autocomplete4.xul b/toolkit/content/tests/chrome/test_autocomplete4.xul
index cbd2adf7cab4..db520331807b 100644
--- a/toolkit/content/tests/chrome/test_autocomplete4.xul
+++ b/toolkit/content/tests/chrome/test_autocomplete4.xul
@@ -13,6 +13,7 @@
 <textbox id="autocomplete"
          type="autocomplete"
          completedefaultindex="true"
+
          onsearchcomplete="searchComplete();"
          autocompletesearch="simple"/>
 
@@ -143,6 +144,13 @@ const tests = [
     result: "Result",
     start: 6, end: 6
   },
+  { desc: "TAB key should confirm suggestion when forcecomplete is set",
+    key: "VK_TAB",
+    removeSelection: false,
+    forceComplete: true,
+    result: "Result",
+    start: 6, end: 6
+  },
 ];
 
 function nextTest() {
@@ -181,6 +189,8 @@ function searchComplete() {
   is(autocomplete.value, "result",
      "Test '" + currentTest.desc + "': autocomplete.value should equal 'result'");
 
+  autocomplete.setAttribute("forcecomplete", currentTest.forceComplete ? true : false);
+
   if (autocomplete.selectionStart == 2) {  // Finished inserting "re" string.
     if (currentTest.removeSelection) {
       // remove current selection
diff --git a/toolkit/content/widgets/autocomplete.xml b/toolkit/content/widgets/autocomplete.xml
index d12c55b92487..c88b6d30a802 100644
--- a/toolkit/content/widgets/autocomplete.xml
+++ b/toolkit/content/widgets/autocomplete.xml
@@ -464,6 +464,8 @@
                   cancel = this.mController.handleKeyNavigation(aEvent.shiftKey ?
                                                                 KeyEvent.DOM_VK_UP :
                                                                 KeyEvent.DOM_VK_DOWN);
+                else if (this.forceComplete && this.mController.matchCount >= 1)
+                  this.mController.handleTab();
                 break;
               case KeyEvent.DOM_VK_UP:
               case KeyEvent.DOM_VK_DOWN: