I know some people are still interested, but here is a sidebar version written in XUL:
Even if you don't have an SVG-enabled build, you can still check out the tabbed interface...
There is currently a regression in window settings (they kinda work, but I don't know what exactly is going on), and hyperbola graphing isn't up to par yet. (I'm working on approximating hyperbolas by quadratic bezier curves...)
But the other 3 conic sections work a treat (and parabola graphing has been improved by converting it into a quadratic bezier curve instead of plugging and chugging line-to's).
There are still some problems with graphing functions that approach infinity very quickly as x approaches 0, but I think I have an idea to fix it (at cost of some accuracy for certain window settings - but then again you really can't accurately graph infinity, so...).
When this is finished, I intend to put it in an installable XPI instead of having the sidebar on the server (save some bandwith). Hopefully I can get hyperbolas worked out today, along with the window settings issues.
In the future I intend to add in support to select previously graphed functions, and remove them, as currently once they are grapher, they are permanent. You have to reset everything to remove it, which isn't always preferable.