Does this apply to twitters full-page sign up pop up?
Not mobile.
(I had, at one point, some 2,000 or so personally modified wepage CSS files under Stylish for just this sort of crap.)
so no, it doesn't work on a larger scale. it's like suggesting to hack MS Windows checks if provided licence key is valid in order to use OS. It works, but for narrow audience, and we should discuss about how to solve issue for all users.