Revert iframe protection upon window unload

Fixes #519

lib/iframeProtection.js

@@ -41,6 +41,9 @@
 				return false;
 			}
 		}
+		window.addEventListener("unload", function(){
+			extension.revertProperties(window, "iframeProtection");
+		});
 		return changeProperty;
 	}
 	

releaseNotes.txt

@@ -6,7 +6,7 @@ Version 1.5:
 		- added {empty}, {false} and {undefined} to webGL preference parameters (i.e. VENDOR, RENDERER, UNMASKED_VENDOR_WEBGL and UNMASKED_RENDERER_WEBGL)
 	
 	fixes:
-		- 
+		- protection of DOM manipulations on unloaded windows may break websites
 	
 	known issues:
 		- if a data URL is blocked the page action button does not appear