Рейтинг 5 из 5 звёзд

Incredibly useful. Can't believe this isn't part of Stylish already.

Is there a way to limit the number of backups kept, besides turning them off entirely?

Это отзыв для предыдущей версии этого дополнения ( 

If you're familiar with 'about:config', you can go there and set the preference 'extensions.stylishsync.bakage'. The default is 14 (days).