Perhaps you can fix the broken websites with userContent.css [1][2][3]
[1]: https://kb.mozillazine.org/UserContent.css
[2]: https://superuser.com/q/318912
[3]: https://www.userchrome.org/how-create-userchrome-css.html
[1]: https://kb.mozillazine.org/UserContent.css
[2]: https://superuser.com/q/318912
[3]: https://www.userchrome.org/how-create-userchrome-css.html