yaiNua9o
Actually, my first attempt to fix my problem was to try to find in firefox codebase where it deletes the extensions loaded from sources, either at the end or the start of the session, I supposed, to shunt that "feature". But after a week a free time spent on it, I made no progress. The codebase and the architecture are just too gargantuan to be tinkered with - at least for me.
I don't think there's really a good browser for both privacy and hacking. I use chromium when I have no choice (not sure what you're referring to concerning the disable modal ; if it's an issue with chromium too, I haven't hit it, and I have 11 extensions loaded from sources).
But my "main browser until it's not enough" is elinks (slightly modified by me to fix ruby support and offer a few more api methods to extensions). I can write extensions as simple ruby scripts, doing things like adding native markdown support, allowing to edit local files, adding proper indentation to HN comments, etc. It's the perfect browser for me (and with cookies disabled and js, css and images not fetch nor executed, it's a good privacy browser as well). But of course, you won't be able to use that to buy something on the web. Still, it's surprising how much I can accomplish with just that.