Hi folks, since updating to the latest version Firefox 55, a couple of days ago, I've been having issues uploading thumbnail images to my YouTube videos. I've never had this issue before. Initially, I thought this had to be a YouTube platform issue (and maybe it is partly), but when I logged into my YouTube account using Google Chrome, I had no issue uploading the same thumbnail image to my YouTube video. I've reported this issue to YouTube and Mozilla, however, I thought I'd post this issue here in the hopes of identifying the issue. Generally, once I upload my video to YouTube, it automatically generates three thumbnails. However, I never use any of the three and instead upload my own. I've never had an issue uploading a thumbnail before. So basically when I try to upload the PNG image (which meets the requirements of YouTube), it just spins the loading wheel and does not upload the image (see attached screenshot). So I tried logging into my YouTube account via Google Chrome and I was able to upload the exact same thumbnail without any issues. I would appreciate if your feedback, thoughts, solutions. Thanks in advance and have a great weekend!