Good on them for actually tracking this feature request for over a decade and not just closing it after three weeks for “lack of interest.” Looking at you, every random GitHub project ever.
The downside is that Mozilla tracks thousands of open tickets, most of which are probably obsolete. But who is going to start now with reviewing stuff from 20 years ago? As much as it pains me (I’m still tracking multiple bugs I reported) to say this, but all tickets with no activity for some reasonable time period must simply be closed. Things are _already_ out of control.
No, any open source project needs someone (or multiple people) triaging tickets; either keep them open and make sure they are implemented in a reasonable time, or close them as a 'wontfix'.
Of course, then you'll have the issue of people opening up new tickets for the same thing, and the triagers will have to either point them to the old ticket, or the discussion about whether or not to do it has to be restarted.