Board Thread:Support Requests - Getting Technical/@comment-4018164-20130408105841/@comment-3335785-20130408120209

Firefox has Greasemonkey for scripts. You can use it to import CSS, but importing CSS with js in going to leave a bit of a delay.

For importing CSS 'properly' maybe something like Stylish? I've never come across it until now, so I have no idea how good/bad it is.

The main issues with using these are the extra scripting involved. I don't know if Greasemonkey support jQuery for instance. You also need to target certain domains within the scripts/stylesheets. Essentially, you need some idea of what you're doing before starting to use these.