The most recent versions of the Jmol applet (confirmed in 11.0.RC4) are slow to update the molecular display when you click and drag to rotate or zoom a molecule. This results in a "jerky" display even with very small molecules. This is only observed when the mouse pointer is within the applet. If the mouse pointer moves out of the applet while still holding down the mouse button, the molecule will rotate or zoom without any jerkiness.
This behavior is ONLY observed with browsers that use the Java embedding plugin, specifically Firefox (and other Mozilla browsers) on OS X (tested on 10.4.8). It has been confirmed by other users (Frieda Reichsman).
This behavior is NOT observed with older versions of the applet (10.9.66). It is not known at which point this behavior first appeared. A demo page comparing 10.9.66 to 11.0.RC3 is available at: