[The-Compiler]

There's https://gitlab.com/jgkamat/jmatrix though it's quite an unofficial hack, and I have no idea if it still works with v2.0.0.

I'd really like to integrate something uMatrix-like (with nice keyboard usage) into qutebrowser some day, but so far I didn't get around to it: https://github.com/qutebrowser/qutebrowser/issues/28

As for password managers, as someone already mentioned in another reply, there are userscripts: https://github.com/qutebrowser/qutebrowser/tree/master/misc/...