if you read through all this question you will see the steps i've gone through in making this mess. yes i've been messing with things i barely understand original question follows, with updates below after updating firefox and other software, i closed the computer to allow updates to take effect. there were multiple tabs open in two firefox windows. this is how always shut down my system and just click on restore session when i open firefox the next time. now it will not open unless i make a totally new/fresh profile. if i use a old profile it will not open. if sync a new profile firefox will not reopen. how can i recover old bookmarks, passwords etc. i am running an old packard bell easynote, with Lubuntu 14.04. thanks in advance for you time. steve updates - i also tried un-installing and reinstalling firefox and using killall firefox in a terminal. after that my google skills ran out of ideas. another update - so now i can sync a new profile and reopen firefox. i went through this a couple of times and found i could not reopen firefox after i had entered about:config and toggled gfx.xrender.enabled to false. i had originally done this to stop the address bar being coloured blocks, a problem it seems for some people with newer versions of firefox. a different get around seems to be installing the theme FXChrome allows me to read the address bar and reopen firefox in a new theme. however the sync i have is very old and doesn't contain any current passwords or bookmarks that are useful to me. my hope is that they are still in the original profile. i can obviously re-enter/reset old passwords, but bookmarks/search history harder to replace. so my question now is modified slightly. - if i created a conflict when i updated firefox with the 'gfx.xrender.enabled to false' setting that i was using, is it possible to toggle about:config values from a terminal or such like. as i've said when i am not able to open the original profile and am only left with a blank screen.