Richard Feynman did not (want to) understand the Michelson-Morley
experiment:

The Feynman Lectures on Physics, Volume 1, Chapter 15-1: "Suppose we
are riding in a car that is going at a speed u, and light from the
rear is going past the car with speed c. Differentiating the first
equation in (15.2) gives dx'/dt=dx/dt-u, which means that according to
the Galilean transformation the apparent speed of the passing light,
as we measure it in the car, should not be c but should be c-u. For
instance, if the car is going 100,000 mi/sec, and the light is going
186,000 mi/sec, then apparently the light going past the car should go
86,000 mi/sec. In any case, by measuring the speed of the light going
past the car (if the Galilean transformation is correct for light),
one could determine the speed of the car. A number of experiments
based on this general idea were performed to determine the velocity of
the earth, but they all failed - they gave no velocity at all. We
shall discuss one of these experiments [the Michelson-Morley
experiment] in detail..."

In 1887 the Michelson-Morley experiment UNEQUIVOCALLY confirmed that
"if the car is going 100,000 mi/sec, and the light is going 186,000 mi/
sec, then apparently the light going past the car should go 86,000 mi/
sec":

http://www.pitt.edu/~jdnorton/papers/companion.doc
John Norton: "These efforts were long misled by an exaggeration of the
importance of one experiment, the Michelson-Morley experiment, even
though Einstein later had trouble recalling if he even knew of the
experiment prior to his 1905 paper. This one experiment, in isolation,
has little force. Its null result happened to be fully compatible with
Newton's own emission theory of light. Located in the context of late
19th century electrodynamics when ether-based, wave theories of light
predominated, however, it presented a serious problem that exercised
the greatest theoretician of the day."

http://philsci-archive.pitt.edu/1743/2/Norton.pdf
John Norton: "In addition to his work as editor of the Einstein papers
in finding source material, Stachel assembled the many small clues
that reveal Einstein's serious consideration of an emission theory of
light; and he gave us the crucial insight that Einstein regarded the
Michelson-Morley experiment as evidence for the principle of
relativity, whereas later writers almost universally use it as support
for the light postulate of special relativity. Even today, this point
needs emphasis. The Michelson-Morley experiment is fully compatible
with an emission theory of light that CONTRADICTS THE LIGHT
POSTULATE."

Pentcho Valev