Support for installing userstyles from userstyles.org

[sirn]

Need to find some way to strip out all Mozilla-specific stuffs.

Planned for 1.2.

[sirn]

Idea: also translate -moz to -webkit equivalent. The only problematic one is probably the gradient stuff. Other than that replacing the vendor prefix should just works.

[daenney]

This would be great indeed. The gradient stuff shouldn't be too difficult either, it's just a question of figuring out which statements need to be converted, after that it's basically a 1-on-1 transformation.