They might do updates without changing the ID every time, especially if they have some pattern like a version number means new features, but a bug fix/security patch build might not. But anyway, Aurora is a high speed updating version, so in one sense ID's don't even matter. If you're not hotly following some specific new feature, just roll back down to the stable releases. Those are coming out so much faster than before anyway (much to the chagrin of a chunk of the FF userbase.)