Posted
These changes will use the userChrome.css file to add custom styles to the browser. While this voids your warranty it is very easy to revert (just delete the file) so it doesn’t hurt to try it out.
First go to about:config and set toolkit.legacyUserProfileCustomizations.stylesheets to true. Then create a file called chrome/userChrome.css in your profile folder. You can find you profile folder by going to about:profiles. If you need more detailed instructions userchrome.org has an in-depth guide.
Then you can simply update the CSS to override the default.
/* userChrome.css */
:root {
min-width: 1rem !important;
}
I chose to keep it at 1rem so that I can’t accidentally make a 1 pixel wide window that may be hard to widen again. But if you want to truly remove the minimum be my guest.
/* userChrome.css */
:root {
min-width: unset !important;
}