The X+libpciaccess upheaval in Rawhide is over, so I was able to update my main system, and pull the Firefox 3. It seems noticeably snappier, especially at displaying images. The rendering is improved too. And they fixed that annoying bug with selected lines in Japanese being of different size from those rendered normally. On the downside, the indispensible Flashblock plugin is not compatible anymore.
[zaitcev@s ~]$ /usr/lib64/firefox-3.0b3pre/firefox The program 'gecko' received an X Window System error. This probably reflects a bug in the program. The error was 'BadName (named color or font does not exist)'.
UPDATE: Flashblock 1.5.5 works.
UPDATE: The BadName is actually a font server issue, bug 430416.