As an Opera user you were not very likely to be behind some middlebox. Middleboxes interfering with pipelined traffic was the reason it was never safe to enable by default.
Why being Opera user made me less likely to be behind a middlebox? I installed Opera wherever I was accessing the Internet. I think only place that they had heavy restrictions was a community college which restricted browser to IE, but I was able to use Opera from a thumb drive. Never had issues.
