Firefox+uBO on Fedora/W11 here, with Firefox being my primary browser for close to 8 years. I only run in to an issues maybe once a year, where I have to pop open Edge/Chrome for some random edge cases to work. I've used Firefox on dodgy, overly burdened and hacked together systems with no issues that were memorable.
The only problem I really remember is at one point Firefox having issues under linux when NVIDIA was swapping their main driver over to the "open-sourced" version, there was some performance issues with decoding, not unusable - but it was resolved within a week.
But, this is just my experience.