This is an issue with fire fox and post data.
Heres a scenario to describe the problem:
you go to the search page, and enter search terms, the search page post to the results page, you view the details of a record and hit the back button, the action that loaded the previous page was the search form submit.
Fire Fox security settings prevents the search form submit from happening again, and instead gives this error.
Te best solution is to have a link to the results page on the details page so that the user does not need to use the back button.