A friend was puzzled about how to change the font size of web pages. The resolution of his screen is pretty high, which makes the writing very small. He wanted to increase the font size. I showed him that one can go to the “View” menu and select zoom in, or press the Control key on his keyboard and then the + sign. This action zooms in on the copy, showing the writing larger. Unfortunately, though, the zoomed-in setting is likely to reset to the default one when you exit Firefox and restart it. How to keep the larger font size so that whenever you open your Firefox browser it will show the writing at the size you prefer? 
Here’s how:
Go to Firefox’s Tools menu and select Options.
Select the Content icon.
Use the drop-down menu to select the font and font size.
Some web pages will override your settings. If you want them not to do so click the Advanced button in the same dialog box and then uncheck the “Allow Pages to Choose Their Own Fonts, Instead of My Selections.”