It's not saving the favicons of websites (imported bookmarks anyway)(one exception - the portable apps site; the FF link folder bookmarks also show the icons). Not sure if that's an FF issue or just a problem with the portable version, but I wanted to mention it.
This is one of several problems I've noticed in 3.5 that seems to be firefox-related.
Personally several of things that changed from an operating perspective in firefox 3 leave a lot to be desired - for example the prompt window for the url bar is now very frustrating in the way it presents information, whereas it was perfect in netscape, mozilla, seamonkey, fireflash (firefox's predecessor), firefox 1 series, firefox 1.5 series and firefox 2 series.
There's an engineering maxim that people in development need grasp.
"If it ain't broke, Don't fix it"
Have you noticed editing is always needed for the inevitable typos that weren't there when you hit the "post" button?