Add a way to disable forward and Back for mouse button 4 and 5

Hi, thank you for making this awesome browser!

I would like to request a way to disable the Forward and Back functionalities on mouse buttons 4 and 5, as there is often no way to re-map these buttons for the average user, and being shunted forward and back when trying to use the buttons for any other application besides your browser is quite annoying.

Personally I encounter this problem whenever I play browser-based games on sites such as Roll20 while attempting to use mouse button 4/5 as my push-to-talk button on Discord, and i can imagine a million other scenarios where you might want to use these buttons for something while staying on the same webpage.