TBB-Firefox allows style change on mouseover (JS disabled)
The download buttons in section 2 of [https://tails.boum.org/download/index.en.html] change their text font once when the mouse is moved over them.
I currently have JS disabled by NoScript (by clicking the ‘Forbid Scripts Globally’ option), so this is a change caused by CSS only. I don't know whether that's considered harmful, but I suspect that it is.
The buttons keep their new font until the page is refreshed; then they return to their original font, and change to the (same) new font when mouseovered again. The two fonts have different metrics, and the buttons' sizes change.
(using TBB-Firefox in TBB
2.2.35-10-Linux-x86_64, based on Firefox 12.0 and Torbutton 188.8.131.52)