Hi, If the session is still open it is possible that you can restore recently closed tabs if they were closed. Or to switch between tab groups, check out the shortcuts:Use Tab Groups to organize a lot of tabs

Thanks for your suggestion but the tabs group options are not helpful as the tabs have actually disappeared. I have no idea why this happened. As far as I was concerned I merely dragged one tab out of the main group, thus making a new tab group, named it, and the first tab group with all my tabs (less the one I had just copied out) disappeared. Also the 'restore previous session' option was not available (greyed out) for some reason even though the session was still open. While the session was still active I did make a copy of previous.js and I may be able to use this to restore the tabs but I need to check which file I use to do this. If not I will probably have to manually go through all history for the past number of weeks to find them which is pretty tedious.

previous.js (cleanBackup: copy of sessionstore.js from previous session that was loaded successfully) recovery.js (latest version of the sessionstore written during runtime) recovery.bak (previous version of the sessionstore written during runtime) upgrade.js-<build_id> (backup created during an upgrade of Firefox)

Did you try to set the name of the group(s) to an empty strong to disable the tab group feature?

Thanks for providing the different file names related to tabs and apologies for delay in responding, the vegetable garden needed its spring cultivation!

I am not clear about your question about how to use an empty string to disable the groups feature but I am wondering if I can use my copy of previous.js to restore my original tabs. I tried replacing recovery.js with this copy but the restore previous session option was greyed out so it did not work as a method.

Just to add that I also tried creating a sessionstore.js file using my backed up previous.js as well and I still do not have an option to restore previous session. (There was no sessionstore.js file in profiles before I did this.)

Does about:sessionstore show the list?

Yes, it shows a list of currently open and closed tabs but there is still no sessionstore.js, only an old sessionstore.bak, in Profiles. BTW my Firefox version is 36.0.4

Current Firefox versions do not have the sessionstore.js in the profile folder while Firefox is running, but instead have a recovery.js file in the sessionstore-backups folder. The sessionstore.js file should appear once you close Firefox.

Session data is still stored in the sessionstore.js file in the profile folder. The sessionstore.bak file is no longer used and has been replaced by the recovery and previous files that you find in the sessionstore-backups folder.

You can check for previous versions of files in its properties via the right-click context menu.

Great, with the help of your clarification I got my tabs back. I closed Firefox, found the sessionstore.js file and replaced it with a previous.js file that I had saved when I first lost my tabs and it worked. Delighted. Many thanks.