The addon works well enough for Youtube, and probably most of the other services.
However, there are fairly bad display problems for Imgur, and /gallery/ style Imgur URLs are also not supported, only /a/ ones. I asked for support for these issues, but the addon dev is not responding to support requests for this addon specifically, for whatever reason.
I ended up coming up with solutions to those problems on my own, which I have posted in the discussion thread.
Disappointed in the lack of support by the author.