How to remove the download tab still appearing on videos after uninstalling Wondershare AllMyTube
To properly uninstall Wondershare AllMyTube for Mac you have to remove additionally the following files or folders - besides the app itself:

/Users/[user]/Library/Application Support/MediaDownloadKit
/Users/[user]/Library/Application Support/Wondershare AllMyTube
/Users/[user]/Library/Application Support/Safari/Extensions/AllMyTube.safariextz


If you have no other Wondershare apps you may also remove:

/Users/[user]/Library/Application Support/wondershare


with [user]: your user name

If you usually use Chrome check the Chrome extensions from inside Google Chrome and delete the Wondershare AllMyTube extension. In Firefox check the Add-ons and delete the Wondershare AllMyTube add-on.

Usually the user's Library folder is invisible. To open it use in the Finder's menubar Go -> "Go to Folder..." (shiftcmdG) and enter ~/Library.