diff -ruNp firefox-45.0.2.orig/browser/base/content/browser.js firefox-45.0.2/browser/base/content/browser.js
--- firefox-45.0.2.orig/browser/base/content/browser.js	2016-04-08 01:54:45.000000000 +0200
+++ firefox-45.0.2/browser/base/content/browser.js	2016-04-24 04:35:13.146499537 +0200
@@ -5646,12 +5646,9 @@ function middleMousePaste(event) {
   }
 
   getShortcutOrURIAndPostData(clipboard).then(data => {
-    try {
-      makeURI(data.url);
-    } catch (ex) {
-      // Not a valid URI.
-      return;
-    }
+    var URIFixup = Components.classes["@mozilla.org/docshell/urifixup;1"].getService(Components.interfaces.nsIURIFixup);
+    data.url = URIFixup.createFixupURI(data.url, 1).spec;
+    // 1 is FIXUP_FLAG_ALLOW_KEYWORD_LOOKUP
 
     try {
       addToUrlbarHistory(data.url);