The add-on is almost to the point where I'd consider it a worthy successor to FireGestures. It's not as feature rich, but that's not the fault of the dev - it just won't be able to be as feature rich when Mozilla is limiting what the new API's can do.

That being said, there are a few things that have prevented me from switching over to this add-on before I decide to upgrade to FF57.

I think it needs a little more options for customization. For instance, it lets you directly save an image or bring up the save image dialogue, but it can be a little annoying to deal with. Like a few other add-ons, it defaults to the 'downloads' directory, which isn't what I want. I'd rather have the option to map a mouse gesture to either "save page" or "save image as" instead of "save image." It's a small gripe, but a function I use quite often, so it's a sticking point for me.

Otherwise, I like the direction the add-on is going and I'm keeping an eye on it's development. Given how much FF57 is going to change, I don't plan on upgrading right away, so hopefully waiting and watching will be a good chance for add-ons to iron out and add in new features that can help restore some of the old functionality that we'll be losing when the new API's hit.

ETA: Read the dev's comments below. Good to know! I figured it was probably issues on Mozilla's end. With such a big change coming, there's bound to be issues. Thanks for the heads up.