I recently discovered FireFox's userChrome.css where you can cutsomize about everything with CSS. I tried googling how I can customize the alert box (when I use 'alert()') but I can't find anything. Is this possible?

CodePudding user response：

Welcome to StackOverflow, Normal! According to this answer, Javascript alert boxes are system objects and not modifiable by CSS. However, you should rarely encounter one while using Firefox, and if you're in the process of writing a webextension, it's much better to write your own notification or popup.