Issue 6967 - Hold on to only non-standard style sheets

lib/contentFiltering.js

Index: lib/contentFiltering.js
===================================================================
--- a/lib/contentFiltering.js
+++ b/lib/contentFiltering.js
@@ -132,20 +132,21 @@
   let styleSheet = "";
   if (selectors.length > 0)
     styleSheet = createStyleSheet(selectors);
 
   let frame = ext.getFrame(tabId, frameId);
   if (!frame)
     return false;
 
-  if (!frame.injectedStyleSheets)
-    frame.injectedStyleSheets = new Map();
+  if (!frame.injectedSelectors)
+    frame.injectedSelectors = new Map();
 
-  let oldStyleSheet = frame.injectedStyleSheets.get(groupName);
+  let oldSelectors = frame.injectedSelectors.get(groupName);
+  let oldStyleSheet = oldSelectors ? createStyleSheet(oldSelectors) : null;
 
   if (appendOnly && oldStyleSheet)
     styleSheet = oldStyleSheet + styleSheet;
 
   // Ideally we would compare the old and new style sheets and skip this code
   // if they're the same, but the old style sheet can be a leftover from a
   // previous instance of the frame. We must add the new style sheet
   // regardless.
@@ -156,17 +157,18 @@
     return false;
 
   // Sometimes the old and new style sheets can be exactly the same. In such a
   // case, do not remove the "old" style sheet, because it is in fact the new
   // style sheet now.
   if (oldStyleSheet && oldStyleSheet != styleSheet)
     removeStyleSheet(tabId, frameId, oldStyleSheet);
 
-  frame.injectedStyleSheets.set(groupName, styleSheet);
+  if (selectors.length > 0)
+    frame.injectedSelectors.set(groupName, selectors);
   return true;
 }
 
 function getExecutableCode(script)
 {
   let code = executableCode.get(script);
   if (code)
     return code;