Using the Mozilla Firefox web browser you are not familiar with the default font of the browser or the default font size is too small or too large. To suit your needs, you can change the default font size and font on Firefox.
The following article will guide you how to change the size and font on Firefox.
Step 1: Open the Firefox browser.
Step 2: Select Tools -> Options . Or choose the Open Menu icon -> Options .
Step 3: In Options, select the Content tab .
Step 4: In Font & Colors, select Font in Default font and choose the size in Size, then select OK to save the default size and font.
From now on you can freely change the default size and font on your Firefox browser to suit you. Hope the article can help you. Good luck!