To settle the discussion (I can't locate the original thread) as to whether
or not there are differences between roofing liner (Firestone Rubbergard
line), and pond liner (Firestone PondGard), I called Firestone today

I did the same thing - 6 years ago. I forget the guy I spoke with. There was a
change in formulation for the UV/mold/fungus etc. that was reported to kill
fish quickly. Firestone knew about the stories and their marketing was that it
wouldn't happen with the pondguard. I have no idea if the stories were
substantiated. The bottom line was the pond version didn't have the same
additives the roofing version needed. He was unable to give straight forward
info due to the newsgroup claiming the only difference was the white paint on
the pondguard logo vs. the batch codes on the roofing membrane. The newsgroup
was of the opinion Firestone was breaking the law charging different prices for
the same material. The newsgroup (this one) caused Firestone to get ****ed and
they stopped talking.
I bought one of each. No difference in performance. No dead fish. I was faxed
the MSD sheets too and they were not helpful.
The only liner to ever spring a leak was the pondguard. ;-)