Mypal68 style portable mode

[K4sum1]

The portable mode in Mypal68 is that you just put a blank file named pmprt.mod into (browser executable folder)\browser, and without any external executables, launch commands, or anything, the browser is just fully portable.

I just ported this to my fork of Firefox which is based off of 125. The code should just be able to be dropped in since I only had to barely modify it to get it from 68 to 125.

https://github.com/Eclipse-Community/r3dfox/commit/13694659db1a9536150923cb92c017a95643289d