Did you check the Web Console and possibly the Network Monitor for possible clues about what is going on ? *https://developer.mozilla.org/en-US/docs/Tools/Web_Console *https://developer.mozilla.org/en-US/docs/Tools/Network_Monitor You can create a new profile as a quick test to see if your current profile is causing the problem. See "Creating a profile": *https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems. *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile ---- Try to ask advice at a web development oriented forum. *https://support.mozilla.org/en-US/kb/where-go-developer-support

We are also facing same issue but with normal file upload control also. Reported issue at: https://support.mozilla.org/en-US/questions/1377891