I was under the impression that it was more accepting the othodoxy of Galilean/Newtonian relativety and joining it up with Maxwell's discovery about electromagnetism.

So if the speed of propogation of EM waves is the same no matter your frame of reference (along with all the rest of physics) then the speed of light can't be relative (a conclusion that was aided by the Michaelson-Morley experiment) and what are the logical consequences of that.

If I'm incorrect in my understanding I'd appreciate any correction.