Open source? Probably not, but the new instander beta (only available on telegram) is really promising and works well.

So I see you clearly haven’t heard of i3, sway or hyperland …

Mull browser is also available on fdroid. It is an even better (secure) alternative to firefox as it uses some of tor architecture, from what I know.

op forgot to mention that it is a "provisional, read-only manner,” according to founder Brewster Kahle.