That's really unfortunate and a bad service provider for you. If there is nothing that can be done for that service, you don't need to use that browser as a daily driver, but can just use for the services that you mention. And you need to keep nagging the service provider for support.
This is not just a browser war. It's a war over your rights, your control over your choices, your privacy, what software and hardware you can use. You are already feeling how that affects your life daily, consider this in a mass attack on you.
WEI will enable service providers to decide what firewall you can use, what addons you can have, what version of the browser you can reach their websites, what antivirus software that you need to have, what cpu architecture, which tablet .. This list can go on.
sure this won't start in this manner right away. But I can assure you it will evolve towards more control service providers have on you.
I can't answer any of these. I don't have the knowledge. I am not using Firefox on mobile, only on desktop. (opera mobile user)
However what I can say is, you need to make compromises on some of your convenience to free yourself from a user hostile company's software, or forks of it which strongholds you to their whims. Silicon Valley is trying to profit against your best interests.
Also as a long running Firefox user, I don't get these incompatibilities at all. And if you start using Firefox and increase the usage numbers the incompatible sites would need to reconsider their stance.
There are forks of chromium already like Vivaldi. You can still use them. Unfortunately using them is not a guarantee that Google can't use their usage numbers as leverage while politicing or advertising bad behaviour to other parties like social media.
Worse yet, maintaining a fork is a huge undertaking for a project in the size of chromium. This means in time the fork may struggle to keep up. Or upstream may introduce functions that depends on the bad behaviours and the fork be forced to either adopt both, or adopt none.
I still have trouble understanding the distinction between "a human consuming different artists, and replicating the style" vs "software consuming different artists, and replicating the style".
There is an old cartoon series called "Zican Adam" In Turkey. Which is a slang-ish way of saying "Sican Adam", "The man that shits". It's about a man where in different situations he gets nervous or angry and shits over the perpetrators.
What about https://en.m.wikipedia.org/wiki/Huntington%27sdisease? Repeats of CAG..