diff --git a/toolkit/content/widgets/autocomplete.xml b/toolkit/content/widgets/autocomplete.xml
index 6c301f20ad0f..50eb252368db 100644
--- a/toolkit/content/widgets/autocomplete.xml
+++ b/toolkit/content/widgets/autocomplete.xml
@@ -608,8 +608,27 @@
 
       <handler event="blur" phase="capturing"><![CDATA[
         if (!this._dontBlur) {
-          if (this.forceComplete && this.mController.matchCount >= 1)
+          if (this.forceComplete && this.mController.matchCount >= 1) {
+            // mousemove sets selected index. Don't blindly use that selected
+            // index in this blur handler since if the popup is open you can
+            // easily "select" another match just by moving the mouse over it.
+            let filledVal = this.value.replace(/.+ >> /, "").toLowerCase();
+            let selectedVal = null;
+            if (this.popup.selectedIndex >= 0) {
+              selectedVal = this.mController.getFinalCompleteValueAt(
+                this.popup.selectedIndex);
+            }
+            if (selectedVal && filledVal != selectedVal.toLowerCase()) {
+              for (let i = 0; i < this.mController.matchCount; i++) {
+                let matchVal = this.mController.getFinalCompleteValueAt(i);
+                if (matchVal.toLowerCase() == filledVal) {
+                  this.popup.selectedIndex = i;
+                  break;
+                }
+              }
+            }
             this.mController.handleEnter(false);
+          }
           this.detachController();
         }
       ]]></handler>