Poor performance of script-based SVG animation under Firefox

Hello SVG Experts!

I run AnimatedEngines.com, which uses bitmap illustrations to help explain 
how various engine types work.  I'm now investigating SVG as an alternative 
to the bitmaps.  I'm an experienced engineer but fairly new to SVG.

I have a preliminary animated SVG running fine now, but am very concerned 
about performance under Firefox 3.0.8.

Have a look:

        http://www.animatedengines.com/svg/test.xhtml

I'm animating the objects by manipulating the DOM in a function called by 
'setInterval().'

The page contains separate controls to adjust the update interval 
(animation frame rate) and the RPM of the engine.  The problem is that I 
can't get consistent speed unless I choose an excessively slow frame rate 
under Firefox  It's fine on Safari and Opera.

I have more detail on the page itself, and all the javascript is self 
contained and commented.

I'd love to get your thoughts.

-Matt Keveney
[email protected]