This can be a problem with the file places.sqlite that stores the bookmarks and the history.

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox

I tried individually dissabling add-ons and then saving a known working profile but it still didn't solve the problem. Starting Firefox from 'Taskbar' showed the problem, starting from 'Start Menu' didn't (same profile) - but inconsistent. Right clicking 'start in safe mode' and then dissabling all add-ons solved the problem (for now). This needs to be fixed properly not with a workaround as I want the safety features of some add-ons. Guys - you need to find exactly what is causing this problem.

Can you tell me how to "start in safe mode" and how to disable add-ons?

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

In Firefox 4 you can use one of these to start in Safe mode:

• Help > Restart with Add-ons Disabled
• Hold down the Shift key while double clicking the Firefox desktop shortcut (Windows)

See also:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems