Modern Web design places an emphasis on branding websites using color schemes and fonts, but when a site's eccentric color palette or tiny text size makes the page unreadable, use Firefox's settings to override the Web designer's choice. The default font option won't help with many sites, since it only works on pages that don't specify their own fonts, but another option in the advanced font settings provides a way to specify fonts by style or to ignore the site's fonts entirely.
Open the Firefox menu and click "Options" to reach the program settings.
Switch to the "Content" tab to pick a new default typeface and point size for fonts on Web pages that don't specify their own font preferences. Although serif faces are traditionally considered more legible in print, this doesn't necessarily apply to computer use. Recent versions of Microsoft Office even use a new sans-serif typeface, Calibri, designed specifically for its screen readability. Although created for Office, Calibri is available for use in Firefox. Another good option for reading long hours online is the sans-serif font Verdana.
Click "Colors" to pick new text, background and link colors for websites. To override sites that specify their own colors, uncheck the "Allow Pages to Choose..." box.
Press "Advanced" to customize which font Firefox uses when a website calls for a general category of font, such as a serif or sans-serif font. You don't actually need to obey these categories; feel free to set a sans-serif font as the "Serif" option if you never want to see serifs online. To stop sites from overriding these settings, uncheck "Allow Pages to Choose..." Alternatively, set the "Minimum Font Size" to make sure all sites use text large enough to read without overriding those that use a sufficient size.
Select another character set in the "Fonts For" box, if you read sites in a language with an alternate character set, to pick fonts for that character set. Firefox stores separate font settings for each character set in the list.
Press "OK" on each open dialog box to save your font settings.