It's not possible for the captcha png image to be cached. it's generated when the javascript function calls it. the function forces the browser to request it from the server and since it's not a static image file it always spits out a new image.

Like i said before, it works on most browsers i have tried. even partially works on FF newest version on windows 11. I don't know what to tell you except get a better browser.

If chrome based browsers don't have any problems fetching that captcha image then FF shouldn't either. If it was a cache issue it would affect ALL browsers.