Increase or decrease print size of fonts in Mozilla FireFox

Please only follow these instructions if you feel comfortable editing files. Make sure you create a backup copy before you edit any files! Changing these files is entirely at your own risk.

To change the print size you have to edit the a file named userContent.css. This file is used to change the appearance of web pages.

The page Editing Configuration Files explains where you can find the file on your system.

Initially I couldn't find the userContent-example.css file, but in the end I found it in the sub folder Chrome.

The full path on my system is:

C:/Documents and Settings/[user name]/Application Data/Mozilla/Firefox/Profiles/p2zad4t3.default/chrome

Make a copy of the userContent-example.css file and rename it to userContent.css

Copy and paste the following 6 lines of CSS code to the bottom of the file.

/* Force the use of a x-large size in print */
@media print {
  body {
    font-size: larger !important;
  }
}

You will have to restart FireFox before changes are displayed.

Instead of font-size: larger you can also use different font sizes such as x-large, xx-large etc. See the CSS font-size property at Mozilla Developer Network.

You can also simply adjust the text size of websites you are browsing.