@tapeykatt There it is... My old Firefox installation. The actual version there was 64.0 (2018), and my modern ass updated it to the latest version available. Lastly, I removed the new Firefox installation to maintain the old (and updated) one. Oh, and I installed Librewolf in there, on both Operating Systems (Linux Mint and Windows 10).
Yesterday, after booting Windows on my old dual-booted laptop, I realized I had an old Firefox installation since 2016. One month ago, I installed Firefox without even noticing I already have it installed lol. And after looking at some files, there were files that had Firefox set as its default program to open, and...