Tobin must think himself very clever to have found a supposedly actionable fault in you not specifying to his satisfaction the exact steps to get the source code (which is in fact available, let's not forget that). Well, since apparently he's now wanting you to remove all his contributions from your code, you could play his game and ask him to provide an exact list of his personal contributions so that you could remove them. If he can't be expected to determine which Github code corresponds to which release version, then surely you can't be expected to hunt down his contributions either. In fact it may not even be possible for you to do so, because the fact that Tobin has commited certain code doesn't necessarily mean that he's the author of that code (as opposed to just copying something over from Mozilla, for example); and some of the code he's authored has very likely been commited by other people, like Moonchild. So, let him provide the list and prove his original authorship if that's the path he wants to take. IANAL (I am not a lawyer), of course, and I don't think his claims have merit, but why not have him(/them all) work for it instead of just trying to intimidate people.
In any case it's very unfortunate that Pale Moon people choose to spend their energy on hounding people for pointless reasons instead of improving the (sadly) increasingly obsolete browser. Mypal and Centaury pose no threat to their IP, they're just hounding you to earn some sort of a "victory" and feel better about themselves in the face of losing the game in the big picture. (As a sidenote, I feel I should give some small credit to athenian200 for at least not behaving like a petulant child - which can't be said about the other two, especially Tobin. )
All that said, and regardless of this MCP attack, @feodor2, it actually wouldn't hurt you to properly tag your Centaury releases (in the Mypal repo) and provide a source archive for each release. It is indeed pretty inconvenient to have to go by just the commit dates. You absolutely don't deserve their attack, but in a way you gave them the means to try it by being a bit lazy.