Bug 1586392 - Fix dragging from the expanded urlbar. r=harry

Differential Revision: https://phabricator.services.mozilla.com/D48248

--HG--
extra : moz-landing-system : lando

browser/components/urlbar/UrlbarInput.jsm

@@ -2064,7 +2064,11 @@ class UrlbarInput {
       return;
     }
 
-    // Drag only if the entire value is selected and it's a loaded URI.
+    // Make sure we don't cover the tab bar or other potential drop targets.
+    this.endLayoutExtend(true);
+
+    // Only customize the drag data if the entire value is selected and it's a
+    // loaded URI. Use default behavior otherwise.
     if (
       this.selectionStart != 0 ||
       this.selectionEnd != this.inputField.textLength ||