Firefox 3b3 (released today) seems to have some Javascript updates to it that IMHO seems to make zimbra web interface faster (may just be due to initial excitement). I also noticed site-specific improvements can be made. I'm not familar w/ what would be involved but maybe somebody can offer suggestions for Zimbra-optimized preferences?

See here: Firefox 3 to remember text zoom for specific web sites : Mozilla Links

(and no, it's not just text zoom that's improved