Are you running 29.0.1? If not, please update as there is a fix for this issue in that release that isn't in 29.0.0

Yes, I'm running 29.0.1. Also there seems to be a problem with history restoring, after disabling an extension and clicking on 'restart now' in the extensions menu, Firfox restarted in the startpage and the entry 'Restore Previous Session' was not available in the 'History' menu (greyed out). Please note that 'Undo Close Tab' does not appear greyed out, it just doesn't do anything.

Hello, can you try to replicate this behaviour when you launch firefox in safe mode once? if not, maybe an addon is interfering here...

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

Just tried, same behaviour as before.

Make sure that you do not run Firefox in permanent Private Browsing mode (Never remember history).

• https://support.mozilla.org/kb/Private+Browsing

• Edit > Preferences > Privacy > Firefox will: "Use custom settings for history"
• Deselect: [ ] "Always use Private Browsing mode"

No, the value of 'Firfox will' is 'Remember history' and it also does, manually revoking single entries from the history works just fine.

I should also say that my Firefox was interrupted a few times lately since my laptop battery is broken and the AC adapter gets plugged off easily. But I never referred to problems having to do with Firefox not remembering something that happened *before* an interruption.