Pop-up message: "this page is asking you to confirm that you want to leave - data you have entered may not be saved"

I realize there have been several questions on this topic, even with the same subject heading. The popup generally appears if you're trying to exit or refresh a page but haven't hit post or submit after entering data into a field. It's a good warning in case you've forgotten to do just that. I accidentally restarted Firefox after an update, and when I returned to the site I was working on I got this popup. Which makes sense, because I had entered in a ton of data and hadn't submitted it. However, the page that I was returned to wasn't the one into which I'd entered my data - it was more of a home page for the website. I suspect this is a lost cause, but ... is it at all possible that the browser actually has that data saved somewhere and is waiting for me to complete submitting it? Or is this just a false positive?