Did you make changes to the DPI setting in Windows?

• Control Panel > Personalization : Adjust font size (DPI) or in Window Color and Appearance

Decrease the String pref layout.css.devPixelsPerPx from 1.0 to 0.1 in 0.1 or 0.05 steps to adjust the size of all fonts and other elements in Firefox.

You can also try this:

1. Open the Properties of the Firefox desktop shortcut (right-click: Properties)
2. Go to the Compatibilities tab
3. Put a mark before "Disable display scaling on high DPI settings" to see if that has effect.

Thank you for your reply! I tried the solutions; none worked. I could not find the choice: "Decrease the String pref layout.css.devPixelsPerPx from 1.0 to 0.1 in 0.1 or 0.05 steps to adjust the size of all fonts and other elements in Firefox." I cannot understand why the settings in Firefox would affect those in other programs. Other suggestions?

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.

• Use the Filter bar at to top of the about:config page to locate a preference more easily.
• Preferences that have been modified show as bold (user set).
• Preferences can be reset to the default via the right-click context menu if they are user set
• Preferences can be changed via the right-click context menu: Modify (String or Integer) or Toggle (Boolean)

See also:

• http://kb.mozillazine.org/about:config