Issue 242 - Do not disable user style sheets on unrelated errors

lib/cssInjection.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 62 matching lines @@
     browser.tabs.insertCSS(tabId, {
       code: styleSheet,
       cssOrigin: "user",
       frameId,
       matchAboutBlank: true,
       runAt: "document_start"
     });
   }
   catch (error)
   {
-    if (!/\bcssOrigin\b/.test(error.message))
-      throw error;
+    if (/\bcssOrigin\b/.test(error.message))
+      userStyleSheetsSupported = false;
 
-    userStyleSheetsSupported = false;
+    return false;
   }
 
-  return userStyleSheetsSupported;
+  return true;
 }
 
 function removeStyleSheet(tabId, frameId, styleSheet)
 {
   if (!styleSheetRemovalSupported)
     return;
 
   browser.tabs.removeCSS(tabId, {
     code: styleSheet,
     cssOrigin: "user",
@@ skipping 76 matching lines @@
     response.inlineEmulated = true;
 
   return response;
 });
 
 port.on("elemhide.injectSelectors", (message, sender) =>
 {
   updateFrameStyles(sender.page.id, sender.frame.id, message.selectors,
                     message.groupName);
 });