I'm not a native speaker no and it was never covered in english class.
I know it's a news grammar thing and probably comes from wanting to save space in papers, I still find it very silly and much less readable.
I also find title case pretty annoying but I think I've become more used to it since youtube videos are titled that way too and I spend way too much time on youtube.
Do you have a lot of extensions enabled?
Is your Firefox updated?
Is xmp or docp enabled so your ram is running at the right speeds?
Is hardware acceleration enabled/disabled in firefox?
Have you tried a fresh firefox profile/install? you could try downloading a beta/dev version and testing with that.
However you should really consider using a password manager to generate, keep track of and autofill your passwords. I recommend https://bitwarden.com/ or https://proton.me/pass :)