Question: Weird behaviour of webrick in Firefox

I posted this in another thread after discovering my ActionMailer failures.
Basically my app had everything configured correctly for emailing
someone upon registration. However the emails were not being sent even
though the log file showed no errors and that the mail was sent.
After some frustration I had the idea that possibly it was related to
the server (local) and not the app itself. However before
reconfiguring from Webrick to Mongrel I started the server in RadRails
and opened it's internal brower. To my suprise the email worked.
So I'm wondering if somewhow Firefox running localhost caused the
email failure. I pretty much have the default setup running for the
browser.
Any ideas ?

TIA
Stuart