Also, Google's favicon doesn't display, and I'm 100% sure it has a favicon.

http://www.sporcle.com/ I see the "favicon" in the URL bar when viewing that page, and can save it with a new bookmark.

There is a hidden preference in about:config that might be causing your problem, if you changed the value of that pref to a very small value. Changing that value to 16 or 32 was a popular "fix" for certain problems when Firefox 3 started showing the web site image on Tabs. The underlying code was changed for that display, and AFAIK that tweak isn't needed any longer in newer versions of Firefox. browser.chrome.image_icons.max_size

--- That web page isn't using the traditional favicon.ico image in the root directory of that website. I think this is the image that is being displayed in the URL Bar, according to Page Info > Media = 50x50 px (scaled to 40x40 px): http://profile.ak.fbcdn.net/profile-ak-snc1/object2/1709/84/q79554940009_3051.jpg Unless I missed something when reading the Source Code for that webpage.

While other image formats and alternative locations are allowed in the standards for "website" images, Firefox doesn't always save them, especially when are larger than the 16x16 / 32x32 image size used in the favicon.ico format. Firefox doesn't save the original image in the bookmarks data file, but rather it converts that image to a text based x-image string. http://en.wikipedia.org/wiki/Favicon.ico

Firefox does support that image type, but webpages really need the link rel="icon" type="image/jpg" href="http://example.com/image.jpg" tag to tell the browsers where to find that image. http://en.wikipedia.org/wiki/Favicon.ico#Browser_support

I am able to have that image with a newly saved bookmark by dragging that "icon" from the URL Bar into my bookmarks - that image is saved at the same time as the bookmark. If you save a new bookmark using one of the other methods, the "icon" isn't saved immediately; it is saved when you use that bookmark for the first time. That is where Firefox has the problem with non-"traditional" web site images, from what I have seen.

I get the missing favicons problem only on 'local' pages; those whose URL starts file://...

There's another thread somewhere I saw that suggested disabling the addon Favicon if you are using it. This worked for me and the favicons have returned to mormal