Mozilla is using a mix of Bugzilla, Jira, Github Issues, and $DEITY knows what else, depending on the team or project in question. A good rule of thumb is that

Mozilla is using a mix of Bugzilla, Jira, Github Issues, and $DEITY knows what else, depending on the team or project in question. A good rule of thumb is that for any major system (code hosting, bug tracking, chat, wiki, CI, etc) Mozilla has at _least_ two- one homegrown and/or OSS, another a proprietary service- and a simmering battle over which should be used. Most of Firefox engineering was still on their fork of Bugzilla (https://github.com/mozilla-bteam/bmo https://github.com/mozilla-bteam/bmo) when I left back in 2021.