How to uninstall a firefox update?

I've installed the last firefox update 3.0.10 but the add on spedddial doesn't work. on 3.0.09 speeddial was work fine.

Hi First, i must say it is not recommended to use an older version of firefox, since 3.0.10 has important security fixes. Try reinstalling your addon with the latest version (according to the addon page, it should support .10 just fine: https://addons.mozilla.org/en-US/firefox/addon/4810), or start a fresh firefox profile.

If you really feel you want to downgrade, just use ubuntuzilla install process again, and manually specify which version of firefox you want.