I've been using Mozilla FF and addons a long time. I know to wait for YouTube addon changes, because YT often do change their formats and addon developers have to catch up. I've come here to see if the developer has made a mention of the MP4 download issue or if others are still having this issue and there are a lot of people giving low star reviews...then five 5 star reviews on top of them. In a row. That tells me the reviews are being falsely 5 starred, probably by repeat accounts and possibly by the developer to counter-balance the negative ones. IT IS COUNTER-PRODUCTIVE TO LEAVE BAD REVIEWS WHEN AN ADDON STOPS WORKING AND DECEITFUL TO MANIPULATE WITH POSITIVE ONES. I was considering buying the product for the HD MP3 downloads, but not now. Siyanara.