I think users should direct their attention towards Mozilla. They're the ones who decided that it is appropriate to take the extension down, and they're in the best position to fight it (compared to individual extension developers). There's a chance that this decision was done by a low-level reviewer and does not represent the official stance of Mozilla.

Also, anything that gets (or forces) the actors behind this to issue a takedown request against GitHub is good, because then there's a chance GitHub will tell them to pound sand (sending a strong signal to others that unconditional compliance with such demands may not be the only, or best, course of action) or actively fight it.