Just wondering if anybody here has tried forking Firefox for the purpose of deep UI customization, and if you did how it went or is currently going. I haven’t been able to find much in the way of posts (on blogs or elsewhere) discussing the subject.

I have several browser UI design ideas I’d like to play with, and at first glance a Firefox fork seems like it might be a good option for this purpose. The primary challenge I imagine would be keeping the fork up to date with mainline for security patches.

Is this practical as a side project for a solo dev or will it be a struggle to keep up?