Same problem here. Yahoo is a good, generic example - Yahoo News, Yahoo Finance and Yahoo Mail all have the same "Y-Bang" icon.

It's pretty simple, even in FF4, to customize your app tab favicons.

Because the app tab favicon is generated by the bookmark just...

(1) install this -- https://addons.mozilla.org/en-US/firefox/addon/bookmark-favicon-changer/ (2) view your bookmarks, right click and select the custom image you want (3) restart browser (for new image to "take")

Done.

I'm running Firefox 5 on Mac OS X 10.6.8. The addon you referenced (Bookmark Favicon Changer 1.46) isn't working for me. Supposedly all image types are supported, but when I right-click on a bookmark and select "Change Favicon," I get a popup window where I can search for files on my computer, and all the files are "greyed out" so that I can't select them -- pngs, jpgs, even ico files.

Also, a heads-up for other Mac users: the only way I could find to right click on a Bookmark was via the Bookmarks sidebar. I can't right-click a bookmark on the Bookmarks Toolbar or the Bookmarks list at the far right-hand side.

Try using https://addons.mozilla.org/en-US/firefox/addon/identfavicon/

This addon creates an icon for websites without a default icon.