Since a few days, I have noticed on several, not related pages that a few seconds after loading (maybe onload), sometimes (about 1 time in 50), FF 3.5 swallows the left margin of the body tag (I suspect) and the whole content moves to the left.
Reloading the page or re-entering the address will not help: The margin stays missing. Going to a different page, and coming back helps: The margin is as defined, and stays that way.
I noted this on a few development sites of my own and initially suspected a CSS problem. Just now, I noticed the very same behaviour on a large portal and I am beginning to suspect this is something universal.
Has anybody else experienced this and knows what this is?