If you're open to using extensions, u can use iceraven, it's a firefox fork that allows more extensions and tries to make it more compatible with them, although they might not work. I just checked and redirector that was mentioned on the other comment is available there. I use it as my primary mobile browser.
I think it should be fine to sell on steam and also be open source, ppl would rather pirate the compiled version than compile themselves, maybe some license that disallows redistribution or something, so other ppl don't change a few things and compete with you on steam... Also if it catches the attention of some linux youtubers (more likely if it's OSS i think) it might give you some extra sales.
I'd like to see an update for typescript, go, rust.
First check if anything you're using is on github, accepts contributions and has some open issues that looks simple to solve, or if theres some new feature u want to propose, then follow their steps for contributing.
Don't go looking for issues on stuff u don't use or don't plan to use, or at least some friend/family uses, it'll feel like a chore and you will have to spend a lot of time figuring out how stuff is supposed to be used what anything does and why...