When trying to upload a custom thumbnail for Youtube for the past week or so, the upload process perpetually hangs, never completing or failing and giving an error. (Or when trying to upload a screenshot here on this support forum.) Similarly, when trying to upload an image to Twitch for the "stream is offline" banner, it just fails every time. Both of these work just fine when I switch to a different browser. (In this case, Microsoft Edge, since it's default and I didn't want to install another one.) Clearing my cache didn't work. Restarting with add-ons disabled didn't work. Windows 10, 64bit Firefox 55.0.2, 32bit (I didn't know until I checked the details, and will switch to 64bit later today, probably.)