I don't have Firefox installed on any of my Macs, and I have no idea what NoSquint is or does, but it stands to reason the NoSquint preferences are stored somewhere on your system. Perhaps in a plist (property list) file or even in a cookie. The old trick of moving the settings file to the desktop to force its recreation has worked for many years and might work in this case.
The trick is discovering where the settings are stored, but that should be doable with FindAnyFile
or the right combination of settings in Finder's Find function.