closes #1328
This PR adds Debian support for all of the Firefox packages.
(Note: Most of these use the GPG_KEY_ID variable, which currently doesn't work in Sid, Trixie and Plucky. #1434 should fix that.) Edit: #1434 has now been merged.

firefox:

Switches from the PPA to Mozilla's apt repository.
Edited ARCHS_SUPPORTED variable to remove the extra Archs that aren't supported by Mozilla's repo.
Looking through the PPA page, it looks like they've only been building for amd64 and arm64 for a while now. So we aren't actually losing anything by switching.
#1427 would need to be merged in order for this to install properly in Ubuntu Jammy and up. But this is also true of the current firefox package. Edit: I'm going to mark this PR as a draft in the meantime.

firefox-beta, firefox-nightly, firefox-devedition:

Edited ARCHS_SUPPORTED variable to remove the extra Archs that aren't supported by Mozilla's repo. The other Archs were only applicable to the PPA, which these packages never used anyway.
Removed CODENAMES_SUPPORTED variable, so that all codenames are supported. I have tested that they all install and run in Buster and up, and Focal and up.

firefox-esr:

Added Mozilla's apt repo for AMD64 machines. Their repo doesn't have an ARM64 version for firefox-esr, like they do for the other Firefox editions. So for ARM, the PPA will continue to be used.

If desired, I can replace the PPA="ppa:mozillateam/ppa" line with

ASC_KEY_URL="https://keyserver.ubuntu.com/pks/lookup?op=get&search=0xaebdf4819be21867"
APT_REPO_URL="https://ppa.launchpadcontent.net/mozillateam/ppa/ubuntu ${UPSTREAM_CODENAME} main"
APT_LIST_NAME="mozillateam-ubuntu-ppa-${UPSTREAM_CODENAME}"

(It's not clear if it was decided to allow splitting methods or not, Since #1295 was merged instead of #1309.
I don't know if that was an intentional decision or perhaps just the first of the two PRs that Martin happened to encounter.)