Start Firefox in [[Safe Mode]] to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes). See [[Troubleshooting extensions and themes]] and [[Troubleshooting plugins]] If it does work in Safe-mode then disable all your extensions and then try to find which is causing it by enabling one at a time until the problem reappears. You can use "Disable all add-ons" on the [[Safe mode]] start window to disable all extensions. You have to close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit") See also http://kb.mozillazine.org/Locked_or_damaged_places.sqlite

I've just disabled the Foxlingo extention and it's back to normal. (tools-addons-extensions and disable Foxlingo)