Rated 5 out of 5 stars

by bachmaj on July 23, 2020 ·

Was great. Stop complaining about it being gone. Research and fix the problem yourself.

See https://support.mozilla.org/en-US/questions/1198055

"Use the userChrome.css file for both Thunderbird and Firefox on my Linux boxes, since support for this add-on in Linux was dropped some time ago.

Create a folder in your Firefox profile named chrome

In this folder, create a text file named userChrome.css

In that file place the following code:

/*
* Do not remove the @namespace line -- it's required for correct functioning
*/
@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* set default namespace to XUL */

/*
* Make all the default font sizes 9 pt:
*/
* { font-size: 9pt !important; }
Obviously, edit that font-size: 9pt !important; to a value that suits you. I generally use the same point size as was selected in the OS's desktop settings. You can also set the font face here, e.g.

/*
* Make all the default font sizes 9 pt:
*/
* {
font-size: 9pt !important;
font-family: Arial !important;
}
A similar file named userContent.css in the same chrome folder can be used to set the size of the content of webpages (and of email if used with Thunderbird.)"