How can I set Firefox to always zoom in on pages automatically?

I just got a computer that has a screen resolution of 1366 x ??? pixels. The screen is also 3 inches wider than my old computer. Anyway, websites show up much smaller than they used to on my old computer, and are hard to read because the text is small. I can zoom in and this makes the text bigger, but I have to zoom in on each individual page every time I look at a page, and this is too much work. I tried to set the default display text size, but that did not seem to work. It works on some pages but not on most of them. How can I set Firefox to always display pages zoomed in? Thanks.