On Linux, I'm using Firefox as my main browser and Vivaldi as my secondary browser.

On android, some of my devices have Firefox, some of them have Fennec F-Droid and the devices that don't have very much storage space have Via Browser. If you're wondering why I have both Firefox and F-Droid's Fennec, it's because I used to just use Fennec but then at some point F-Droid announced that Fennec was outdated and it was missing several security updates that were present in Firefox. I switched to Firefox on the devices I use browsers on more actively but I didn't see a reason to switch all of them.