More anedoctal evidence: at my job, some windows users who access
GNU/Linux and AIX servers via Putty, regularly use "copy on select"
(which Putty provides) and do *love* *it*!

Since Windows doesn't have the concept of pasting the PRIMARY buffer
with the "middle button", Putty uses the right button for it.

There is also another argument against changing this behaviour on
Firefox:

 1. fix consistency for Windows Firefox users
 2. break consistency for all GNU/Linux desktop users

The hipotetical benefit of 1. is far overcome by the concrete disaster
of 2., IMHO.

Once again, the problem in NOT copy on select, nor paste on middle button. It is "use primary buffer as a link to go to" on middle button click.

Not really that big of a deal, but there is much misunderstanding over what the original poster complained about.