It seems to me that the tag mozilla is not used well, and should be removed. All of the mozilla questions are (or should be) tagged with either firefox or thunderbird, and not with mozilla. Should the tag be removed?
There are still some questions, that are more generic "mozilla" related questions, I have gone through and retaged most that were purely "Firefox" or "Thunderbird" questions.
Can refer to either the Mozilla project or Mozilla Foundation. They produce a variety of software including Firefox and Thunderbird; thus, questions about a particular Mozilla program (versus the organization itself) should use a more specific tag.
As far as removing it, I think it still serves a specific purpose.
What is Mozilla XPCOM and how I install it on ubuntu
Where can I find Mozilla NSPR Package?
So there are some things that seem to be Mozilla specific.
This is in the air (my opinion) as far as the Mozilla usage:
Recover Firefox sync data? This seems mostly to be about Firefox at first glance, but It also is about the Sync service that they provide. May or may not need the tag.