It's probably a bobcat or a coyote. Both of which are common in New England and can be melanistic. Although there's never been a truly black bobcat, they do occur to be quite dark. But both bobcat and coyote have the gene for that mountain lions do not.

There is a YouTube video which may have been taken down. This woman gets her gun because she swears there's a mountain lion in her yard in Colorado I think. She swears up and down it's a mountain lion and she's going to go out and either shoot it or scare it off. As she approaches this cat sitting in her yard it gets scared enough to get up and take off and at that point you can see it's a bobcat. Slightly tufted ears, and a bobtail, and clearly very small compared to a mountain lion. She turned off comments