The fix comes to sid first. (Not counting experimental.) The right way to do it is to run mixed testing/unstable with apt-pinning so that nothing gets pulled from unstable unless spcifically requested.
That said, stable with Firefox from Mozilla’s site and Neovim built from sources and gpack’d into deb package runs perfectly fine with much less hassle.
Idiots Avant! (post-punk, noise, experimental pop)