Mouse's buttons 4 and 5 operate as back and forward shortcuts in Firefox. Accidentally pressing these buttons has been common with every mouse I've owned and has resulted in severe issues with banking websites and job applications. I don't want to disable the hardware keys because these extra buttons are useful especially in games with complex control schemes.
about:configinto Firefox's address bar
- If you haven't previously disabled it, a warning page about the dangers of changing settings that you don't understand will pop up. Read it, then click "I accept the risk!"
- In the about:config search bar, search for
mousebutton. You should find two preferences,
mousebutton.5th.enabled, both set to true. Double click each of these to set them to false.
- Restart Firefox probably. IDK that's what I did, don't know if it's necessary.