If you need to increase or decrease the size of fonts and other elements in the user interface and web pages then increase the String pref layout.css.devPixelsPerPx from 1.0 to 2.0 in 0.1 or 0.05 steps to see what works best. In current Firefox versions this pref is a String value parsed to a float and allows to fine tune the dimensions of all elements (user interface and web pages) more precisely. To open the <i>about:config</i> page, type <b>about:config</b> in the location (address) bar and press the "<i>Enter</i>" key, just like you type the url of a website to open a website.<br /> If you see a warning then you can confirm that you want to access that page.<br />