There is an updated pull request by Duncaen against master on the void-packages repository

https://github.com/Duncaen/void-packages firefox-90
https://github.com/void-linux/void-packages/pull/32002

[ci skip] firefox: update to 90.0.
#### Does it build and run successfully? 
(Please choose at least one native build and, if supported, at least one cross build. More are better.)
- [x] I built this PR locally for my native architecture, (x86_64-glibc)
- [x] I built this PR locally for these architectures (if supported. mark crossbuilds):
  - [x] x86_64-musl
  - [ ] aarch64-musl
  - [ ] armv7l
  - [ ] armv6l-musl

A patch file from https://github.com/void-linux/void-packages/pull/32002.patch is attached