There is no notification of replies to threads that I mark as "watch". Discussion about it: https://support.mozilla.com/en-US/forums/contributors/704587
It would be good to take a fix for this in with the 2.2.3 update, or maybe it's not even code related. But it makes it rather hard to keep an eye on the contributors forum.
Looks like the other bug is only about non registered users, this one is for registered, but maybe the other bug can be used for both cases.