While testing a web page for compatibility when images are turned off, I discovered a handy bug in Firefox.

When I renamed to directory (so the references to images in the HTML and CSS files were broken), and then refreshed, everything went as expected: no images were shown. But when I refreshed for the second time, Firefox displayed the images again. I refreshed again: no images. I refreshed sometimes again, and the images were shown again.

I think that -for some reason- Firefox sometimes shows the images from the cache. But that’s nonetheless useful when testing a website on accessibility.