I believe I found a bug with p:dataTable while investigating a question on StackOverflow (http://stackoverflow.com/questions/8764 ... ean-even-a). The issue is that, when reloading a page, Firefox tries to save changed form values and restore them after reload so that the user does not lose what they entered. Since p:dataTable uses a hidden form element to keep track of the selection, Firefox restores this value. This leads to the rendered selection and the actual selection being different.
I think that the p:dataTable component should either explicitly clear out the hidden input or read the value and render the selection in the table to reflect the hidden input. I personally tested this on FF4 (Mac OS X) and the original reporter said that they'd seen it on FF8, though someone else followed up saying that they didn't see it on FF9.