I tested on that song (Eric Carmen's All by Myself) and it got it on first try, first 5 seconds.

By "open" tab, you mean "active" (as in, the one you're viewing) tab, correct? And you're then clicking the button and see the black bar on top of youtube, right?

Did you get "No result - 1001", or something else?

The server this addon uses by default is in Europe. I'm thinking, that if you're far away from EU, then there will be quite a bit of ping. That could possibly mess things up, though I'm not sure how.

If you are up for some testing, then please make your own account on acrcloud.com and try it with that. There's more info on that on the preferences page. It's free.

Thanks for the review.

EDIT 6/2: Thanks for your clarifications. The problem is, as you described, that it was a live version and had alterations.
If you were to create your own ACRCloud account and used the "recorded audio" checkbox, you might have better results with live performances. Though, I'm not sure if that will degrade results for studio stuff. Find further info in the add-on's preferences page, if you're interested.

If you want help then I'm gonna need a bit more details, like "which website I tried it on" and "my Firefox version is..". And "what went wrong" would be a nice addition too.
I've written down few steps for a trial run on the addon description, if you would try that.

If it's the extension, then unfortunately it isn't feasible for this addon to work on it for now.