Quantum is simply a project name, which covers a whole range of of performance improving projects.

Quantum came into reality with Firefox 57, so any version after that has the "quantum" projects included. So yes, the current developer edition includes project quantum

The Firefox Developer Edition is a reskinned version Firefox Beta, with a greater focus on development tools. All of the Firefox channels (Rapid Release, Beta, Nightly and Developer Edition) are now considered "Firefox Quantum".

Quantum is just the project name of the latest big Firefox redesign that occurred in Firefox 57. This is similar to how Firefox Australis was the project name for the big Firefox redesign before that.