My 2 biggest beef with Firefox is website compatibility and dead tabs.
For item 1, certain sites don't work with Firefox when they do with Chrome. This can happen even in sites of industries that claim to want privacy / decentralisation / anti-monopoly. Some of these are government websites.
Sometimes, websites explicitly block non Chrome browsers too.
So if I had to request a feature, this would be it.
For the second item, I haven't been really able to pin it down. But I've seen this on both Android and Linux version. A tab sometimes goes dead, that it it doesn't refresh or basically doesn't respond when typing a new address. The solution has been to just close the tab and start a new one.
Will give it a try and provide more feedback