I've been using FF for more years than I care to remember, and with the exception of a couple of sites that weren't really that important, I've never had an issue. I certainly never had an issue running uBlock Origin and YouTube.
I flat out refuse to use anything even loosely based on Chromium on principal alone.
Connect the Steam Deck to a compatible dock and you can quite easily use it as a desktop. At the end of the day, it's still an x64 based PC that's just handheld.
Linux user here running FF, no real dealbreaker issues at my end.
I use Mozilla every single day and have done so for about 6 years now. Personally I don't feel like I'm missing out on anything but ads if I don't a Chromium based browser.
I've got plenty of old software here under Linux that still runs fine to this day across a number of PC's and even a Raspberry Pi that I use as a backup desktop. I honestly can't see backwards compatibility being any more of an issue than it is under Windows - There's a number of accounting packages released under Windows 7 that won't run under Windows 10, the latest version of most popular browsers won't run under Windows 7. Likewise, the latest version of MS Office 365 won't run under Windows 8.
RTX has worked under Linux both natively and via and Wine/Proton/DXVK/VKD3D for quite some time now.
Now all they need is a complete nvidia-settings application under Wayland that allows for coolbits to be set, and I may be able to use Wayland. For some reason, my RTX 2070S boosts far higher than the already overclocked from factory boost clocks, resulting in random crashing - I have to use GWE to limit boost clocks to OEM specs to prevent crashing.
Strangely enough, this was never a problem under Windows.
Fresh install, KDE Neon 6.0.0 user edition:
I find the opposite running KDE Neon. In fact File Explorer 'lag' is a widely expressed issue regarding Windows 11.
Find a new job before those new owners take over the business.
I never stopped using Firefox, and I never had a problem with anything but Government sites.
Did my part. If I have to run Windows along with a root kit to play a game, I'll stick to Linux.
TBH, the game wasn't really that great to begin with.