Are you sending HTTP response headers that instruct Firefox not to cache the pages?

You can get a "document expired" message if you use the back button to return to a specific page and the web site has instructed Firefox not to cache the page.
Firefox tries to retrieve the page from the server, possibly by sending POST data.

Thank you.

you mean my form post the data thats why the problem is occured ?

but my other site is working well and its not display this error.

i have same second site.

any other reason for this message Please.

Thank you.

Suggestion:

Instead of clicking the "back" button, right-click (or click-hold) the "back" button to get the contextual menu and then select the previous page to go "back to".

Thank you for suggesion.

i tryed as per your suggesion.

but also its display same alert message.

any other solutions Please.

Thank You