Installed as part of the vdownloader.com installer. I don't know what it does, but it bypasses about:newaddon. ID: Player@Wondershare.com
Hm. Actually, it looks like these were probably installed by the Wondershare installer rather than vdownloader.com. No add-ons showed up immediately after that install so I didn't reset my VM.
The developers have been contacted.
Closing this. This is a very old report, the add-on hasn't been signed, and more recent add-ons from the same developers look legitimate.