You must read the disclaimer before downloading.
From the Developers:
Are you always changing the text zoom level when you open a new browser window? Do you find some sites you visit have impossibly small fonts and you are constantly changing your text zoom back and forth as you visit different sites?
NoSquint is a Firefox extension that allows you to adjust the
default text zoom level, which is very useful if you have a small
display or run at a very high resolution. NoSquint also remembers the
zoom level per site (though you can disable that). Until website
designers (typically those who know of no life outside Internet
Explorer) who insist on using
font-size: 50% are administered a harsh LARTing, NoSquint exists to make web browsing tolerable in Firefox.
You can view the Online Help to get a sense of the features NoSquint supports.