Firefox Àpèjọ Àtìlẹ́hìn

I use Linux, but know nothing about it. My brother installed Mint on my desktop; he was my Computer Guru, but he has passed away. I need to update from FF88 to at least 99. Can you help me, please? Many thanks if you can.

If I try to access https://bugs.cacert.org I get an error message: SSL_ERROR_EXPIRED_CERT_ALERT

If I access to the same site with chromium browser, there is no such error message, even more: I can access the certificate with the following information: valid until 2024 (see complete cert as picture).

Why this obviously wrong error message? How can it be circumvented (a warning might work, but a blockade?)?

Dear, I always have a lot of tabs opened and I guess I had one too many opened yesterday. Already I had to recover my settings after a crash the day before. So I had the crash and restarted the pc yesterday evening. All my tabs were gone, so I shut down the pc and started up again this morning and still no sign of restart or nothing of my tabs, history, all my Linux worksheets were completely empty accept for this page... I went to settings to restart the previous settings but it always does that automatically, and it only started the one I was in this morning (the empty one) I tried for a crash rapport but could not find one. How do I get everything back, please ?! I need to get the tabs back before this previous session! Please help... Where can I find them? What can I do? I can't have lost them all ... I will go nuts .. Please help me! My system is a Linux Mint 21.0 version, I think Thank you so much! Nadine