This keeps happening - not an isolated incident. The option to open a dialog box to upload a file becomes non-existent. Concurrently, I'm unable to download and save files. This is resolved when Mozilla releases an update and I can update my browser. Then eventually something happens and the features stop working. It's like a download fails and then blocks further ones. However, there isn't something obviously stuck in my downloads history. I can't seem to close my browsers and reopen it to fix, have to wait for an update but this always resolves it. This has happened at least a dozen times now. It is NOT my operating system. This is wildly frustrating.