Open source? Probably not, but the new instander beta (only available on telegram) is really promising and works well.
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.
And if you are on Android, use YouTube revanced.