Hmm. It's odd for something to be archived without a solution.

I noticed in your screenshot your browser is being managed by your organization. If this is a problem;

Your organization has disabled the ability to change some options

https://support.mozilla.org/en-US/questions/1256411#answer-1213977

https://support.mozilla.org/en-US/questions/1256411#answer-1214022

https://support.mozilla.org/en-US/questions/1239094

Session restore tries to

You may have corrupt sessionstore [v56] sessionstore.jsonlz4 file(s). Delete all sessionstore* files and the sessionstore-backups folder.

Don't delete the files if you need to rescue any data from them, just move them out of the profile folder to some location where Firefox doesn't look for them. You can try to read out their contents using this tool: https://www.jeffersonscher.com/res/scrounger.html

Type about:support<enter> in the address box.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder

Linux: Under the page logo on the left side, you will see Application Basics. Under this find Profile Directory. To its right press the button Open Directory.

Locate the above file. Then rename or delete it. Restart Firefox.

I manage my PCs but as I have 3 at home I suspect this is where the ‘browser is being managed by your organisation’ comes from. I’ll have a look at the second option later. Thanks for the responses.

Note that you appear to have a user agent that is modified by Avast/AVG Anti-Track () that could cause problems on some websites, so if you use this software and notice issues then try to disable this software. You can contact Avast if their software causes problems for you. We can't do much about this apart from identifying Avast/AVG Anti-Track as a possible cause.