Is about:config > app.update.auto set to '''false '''sufficient, [https://www.google.com/search?client=firefox-b-1-d&q=firefox+disable+update+prompt#fpstate=ive&vld=cid:0bd85db1,vid:nD-oXxrCCRs,st:11 How to Disable Firefox Update Notifications: A Step-by-Step] Or how about the registry? [https://connect.mozilla.org/t5/discussions/turn-off-update/m-p/31890 Turn Off Update]