ajax cache problem in firefox 4

For some reason Firefox 4 is not updating ajax content. It seems to store cache until t开发者_StackOverflowhe cache is manually removed. I am using must-revalidate headers and each request sends an expired time, so what can be causing this issue?

Some debugging revealed that firefox doesn't do actual requests if an expire time is set in the future.

It'll only start doing requests when the expire time is in the past. This means that the usual manner of getting 304's doesn't work because they never actually get requested.