I really hate not having a thorough test-case, but I really am
mystified by this.
I'm running Firefox 3.0.5 with firebug. This page (test case):
has a super-minimal, unstyled jQuery + jQuery UI tab.
The page doesn't do anything unsurprising - until you 'suspend'
firebug (right-click the little bug at the bottom and 'suspend').
Reloading the page will cause jQuery to reload parts of the page every
few seconds (check your HTTP headers), cause the CPU to spike and
generally to cause oddness.
I'm sorry I can't be more specific, I have no idea if this is a jQuery
issue, a jQuery UI issue, Firebug or Firefox - although clearly it's
related to Firebug. I have tried it on two machines, so it's
definitely not just me :)
Until I worked out this was related to suspending Firebug I was
tearing my hair out trying to nail this down. I'd be interested first
of all if anyone can reproduce this.