As per https://endoflife.date/firefox 78 ESR has been EoL for nearly a year soon. According to a quick grep -r only the following consumers remain:

• 0ad
• cjs
• polkit

This would also contribute to #38229 (mozjs78 has python-devel in makedepends).

We should also keep in mind what happened with mozjs60: 5121c0f (mozjs60: re-add as meta to allow people to upgrade their systems) so the same thing doesn't happen again with the removal of mozjs78.