Not for nothing, it is standard legal boilerplate. I just checked two randomly selected terms of service--one for ReadAI, the other for Google--and they both include a very similar clause with those exact parameters.
That said, I'm not suggesting Mozilla isn't also being wildly hypocritical in their behavior, and hamfisted in their PR.
Both of your examples are cloud services, not software run locally on users' own hardware. If they intend the license to be limited to cloud services like Firefox Sync, then they should say so.
That said, I'm not suggesting Mozilla isn't also being wildly hypocritical in their behavior, and hamfisted in their PR.