Note that you can make such rules work domain specific or URL specific with an @-moz-document domain

Note that you can make such rules work domain specific or URL specific with an @-moz-document domain(){} or url(){} block.

https://developer.mozilla.org/en-US/docs/Web/CSS/@document

@-moz-document domain(support.mozilla.org), domain (xxxx){ body, body * { font-size: 1em !important; } }