I saw this happen in version 41 of Firefox, but I am sure this has been an age old issue. The events are getting triggered from multiple levels in Firefox. I had faced 2 instances of the same (but for 2 different reasons).
Recent one was because there was a
method that was defined for
link_to. This generated a
data-method is added to the generated
a tag. This was resulting in two clicks to be fired from the same a tag.
If this is a
get request you are lucky, just remove it. I am not sure what to do if it is any other verb.