Zorin16-Linux version 99.0 Ubuntu Canonical 1.0, -found in Help/About. Firefox recognition of version below says 91.0. Also have Linux Mint 19.3 (Tricia). Computer 15YO Dell Dimension 900. I've had no problems with Linux Firefox for many years. I do not use any other Non-Linux OSes. Linux Mint updates Firefox regularly and so do I in that OS. I'm currently in a free version of Zorin which doesn't seem to push out updates, so my Zorin Firefox may be sadly out of date. At any rate, today in Zorin, when I went to several of the bigger online sales platforms, they refused to accept my Firefox and suggested Chrome, Opera, and Safari; Target suggested Firefox. Went to Mozilla to try and upgrade, but it didn't offer the Linux browser automatically when it read my computer. I was only offered the Windows browser. This may be because the computer is an old Dell Windows machine that I converted to Linux or it may not. I've never had this happen before. Yesterday in Linux Mint, in which Firefox is upgraded at least weekly, the same thing happened once with a big online retailer. They said my browser was outdated and unsafe. What's going on? I'm wondering if Linux OSes are simply not being accepted when the big retailers are doing software upgrades, or is something going on with Firefox?