My FF has been opening verrrry slooooowly for the past few weeks. I happened upon a neat little trick today that really helped.
If you have a slow FF and are on Windows XP, right-click the shortcut for FF and click Properties. On the Compatibility tab, select Windows 2000 and the tickbox for ‘Run this program in compatibility mode for.’
FF was taking about 45 seconds to open; now it takes 2-3 seconds and I haven’t noticed any other differences. Very cool.