I'm tired of defending Mozilla here, so I have to say that working on their web browser is not a priority for them. In fact, it seems like they're interested in everything _but_ working on Firefox.
The Firefox repo gets 100-300 changesets per day, up to 1000 commits per week. Around 100-150 contributors land those in any given week. That's activity comparable to Linux or Chromium. And, the release schedule is accelerating from a four-week cadence to a two-week cadence this fall.
Just because other efforts and initiatives are flasher or noisier doesn't mean Firefox isn't the main priority.
Just because other efforts and initiatives are flasher or noisier doesn't mean Firefox isn't the main priority.