FF Dev edition is indeed more "stable" than current stable version. In terms of extensions, at least the ones I use, they are fully supported.
57 also has a lot of under the hood improvements and I strongly recommend. Only reasons I do not use it on my systems is simply because if something breaks, I have to spend some time to fix it, so I myself am waiting for official 57 release to install it in most of my systems.
NPE ZAM and KVRT are good opinion scanners, but one must ask: how often do you use it? if it is rarely, then keep one. if it is often, then all 3 good enough.
One recommendation if you will in terms of extensions: Don't track me Google <-- use it if you want to bypass the long google link when you search on google and simply copy the link. Not sure if its working for FF dev version but you could try.