Heratech

See this article: http://lifehacker.com/5344418/make-firefox-faster-by-vacuuming-your-data...

'Firefox tip: Firefox 3.0's Awesome Bar added all kinds of features to the 'fox, but unfortunately it's also created some performance issues—for example, by upping the default history time, leading to larger, fragmented databases. This quick hack speeds things up.'

but don't do what they say, use this extension instead:

http://lifehacker.com/5347125/vacuum-places-improved-speeds-up-firefox-w...

Vacuum: https://addons.mozilla.org/en-US/firefox/addon/13878