Hmm, Firefox might not save data you entered on a form to the disk cache; it might only store the page that was sent from the website. I don't know how to test that...

Did the site display a confirmation page with your information on it, or just a brief "thank you" kind of page?

Firefox does keep some form data in memory so you can use the Back button to return to a partially filled or submitted form -- assuming the site doesn't bar browsers from storing that page -- or to preserve your input if you close the tab accidentally -- Undo Close Tab should return you to where you were.

You could check Firefox's History menu for closed tabs and closed windows to see whether you can find that tab again and re-open it. By default, Firefox only remember the last 10 closed tabs per windows, and the last 3 closed windows, so it might be too late by now if you have been using Firefox heavily...

Thanks a much jschesr2000,

Your answer doesn't seem to resolve my problem, but I've installed some add-ons to Firefox that will probably help me in the future, if I have to fill up some "forms" (on reality some e-mails you send from a webpage to your provider that you can't have copy of) .

So Firefox cache doesn't keep a copy of the forms you have filled (otherwise the forms you have just filled in, and lost the connection, and want to get back to). Even if the website I've filled in has a verbose (but hexadecimal) cache, I can't retrieve it. What a pity. Knowing that if they make a form to contact them, it's to avoid you from having e-mail trace of the information you transmitted them, as they never give a direct e-mail to contact them. As an example, I can tell you that I already wrote them a form (a social security center for students), they answered me (an incorrect information dating from 2008) and in the "original mail information", I found my coordinate, but not the original form I sent to the center -- they clearely deleted it (or probably kept it to themselves).

You (Americans) are probably blaming me for being a heavy smoker. 1 and a half pack a day. But I'm trying to quit. Not for medical reasons (although it would be reasonable, although I'm not tired after a 7-floor stair climb) but for money reasons: my 1+1/2 pack a day cigarette consumption (USD 11,7) ruins me. But this have nothing to do with the cache problem. Moreover in the US your tobacco struggle is even more harsh than in the EU, so your cigarette price increase is even stronger than here.

Let's say in the about:cache Firefox page the I've found an hexadecimal page, long enough to correspond my completed form to the social security insurance. Would there be a way to convert back the hexadecimal code to readable text in order to know what exactly I wrote to the insurance, whatever they say I wrote ?

Thank you in advance, Andreï

Hi Andreï, could you open the following: type or paste about:cache in the address bar and press Enter. Under disk click the link to List cache entries. This may take a long time.

Eventually you should see a list that lets you find the URL you're trying to decode. If you click it, Firefox should show the content there and list the compression type, which most often will be:

Content-Encoding: gzip

In that case, if you save the encoded content to a new file with a .gz extension you should be able to decompress it using your favorites ZIP utility. Of course, finding the beginning and end of the content may not be intuitive. I don't know whether the cache entry info page is helpful or not.