855910 - Don't erroneously revert to using /favicon.ico as the tab favicon on some pages when navigating back in the middle of a document load

Status: RESOLVED INVALID

(Firefox :: Tabbed Browser, defect)

Description

[Frank Yan (:fryn)]

Steps to reproduce:
1. Navigate to a page on Wikipedia, e.g. http://en.wikipedia.org/wiki/Wikipedia#External_links
   - The page contains a <link rel="shortcut icon"/>, and the tab displays the image at that path, as verified with DOM Inspector. 
2. Navigate to another page, e.g. the "Video of TED Talk by Jimmy Wales on the birth of Wikipedia" link, that may take a few seconds to load.
3. Immediately after the page navigation is committed (the location bar changes value to page B's url) but before the page finishes loading, navigate back (e.g. via the back button or alt/cmd+left).

Expected result:
The tab once again displays the image at the <link rel="shortcut icon"> path.

Actual result:
The tab displays the image at /favicon.ico.
(Verify with DOM Inspector.)

I'm not sure if this happens on any other websites.

If this is indeed a legitimate bug on our side, I suspect that this bug has something to do with mTabProgressListener's onStateChange, in particular the following lines:
  if (!this.mBrowser.mIconURL)
    this.mTabBrowser.useDefaultIcon(this.mTab);