This morning when I opened Firefox, instead of opening my many windows and tabs from my previous session as usual it opened only my homepage. There was some message about it having difficulty and suggesting I do a reset of Firefox, which I wasn't interested in doing. I didn't pay it much mind at the time. I am running Windows 10 Pro 64-bit with latest updates on a Desktop computer and I use Windows File History backup system to backup the sessionstore-backups folder of my profile, among others. However, when I tried to replace sessionstore.jsonlz4 with a renamed recovery.jsonlz4 or similar from any of my many backups (after quitting Firefox), when I reopened Firefox it just opened my home page. The files are about 113 KB. I tried replacing sessionstore.jsonlz4 with one of the much smaller files from today's browsing and they worked ok. I wasn't allowed to attach one of the files here. I'm a bit peeved as it seems I've lost all my windows and tabs, and I thought I'd protected myself against that eventuality, at least in such an apparently simple and mild mishap. Any suggestions on getting my tabs back? Thanks, Paul