That's correct, as long as no userscripts are installed, Greasemonkey
doesn't do anything except from being there and waiting for a script file.
What kind of "formula images" though? Really images, or just making it
visible?
SVG? PNG? BMP? HTML?
There's plenty of userscripts for LaTeX input, pick the one(s) you need,
not sure if it's there:
http://userscripts.org/scripts/search?q=LaTeX&submit=Search
Chris