This happens with every image, whether the website is properly cached or not. Firefox insists on re-downloading the image instead of fetching it from the memory/disk cache and I find that behavior to be unacceptable. I have already tried: Changing browser.cache.check_doc_frequency to 0 or 2 and setting browser.download.manager.scanWhenDone to false. The second actually worked for a while when this first started happening, but then it started again, probably after one update or another. I don't want an add-on specially for this (unless it actually works with the usual save/save as functions), this should be a default or at least toggle-able behavior for any browser.