Seems to still be available on F-Droid, but the last update was in 2017. I’ve installed it, but ended up not logging in since it’s targeting an SDK version so old that Android is giving me a bunch of warnings (and it doesn’t even scale to my entire screen, there’s a big black space at the bottom)
I thought it was a problem with my phone since I’m using a custom ROM and it did not happen before. When I open Firefox and it has been in the background for a while, it shows a black screen where the web content should be and often crashes if you try to open another tab or do something else. Also happens if I open a link from another app. The only solution is to close Firefox and swipe it off the recent apps and reopen it. Is this the same problem you have?