NPAPI plugin making JavaScript calls causing spurious "Unresponsive Script" warnings

Test environment: Windows XP SP2, FireFox 2.0.0.11

While implementing an NPAPI browser plugin, we have found something we
think is a bug with the way FireFox detects unresponsive scripts. We
started getting "Unresponsive Script" messages while the plugin was
regularly calling a very small JavaScript function on the page, which
is in charge of updating some kind of progress dialog.

That function is very small, the first thing I did was to add timing
around the call, and it never exceeded 30ms. However after the plugin
had been calling that function for about dom.max_script_run_time, we
were getting the warning.

After a few hours of experimentation, I realized that I could avoid
the warning to trigger if I was calling a different function on
regular intervals, and have it issue a setTimeout call like so:

function OnHeartbeatTimeout() {
    console.log( 'OnHeartbeatTimeout' );
}

function OnHeartbeat() {
    console.log( 'OnHeartbeat' );
    setTimeout( 'OnHeartbeatTimeout();', 10 );
}

Just calling OnHeartbeat and returning, or even waiting a bit didn't
fix the problem. It had to be a setTimeout call, my understanding is
that this is causing FireFox to issue a javascript call internally
rather than firing from the plugin, and this effectively resets the
timeout counter so it doesn't trigger.

If someone can give me a few directions, I'd happily report this to
the bug tracker.