I think the corner-peel ad is only optional if you're a paid subscriber, but for pop-ups in general with modern Firefox it's Tools > Options, choose the Content tab and check the "Block pop-up windows"
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— David
Zero Gravitas — 2017 Flying Cloud 26U | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill
My wife just went through the same thing. The old version of Firefox which she had was 3.6.17 which is no longer available. She now uses 4.1. In downloading the add-ons last evening we found that the one which stops the "peel back", Adblocker 0.6.7, does not run on Firefox 4.1
Adblock Plus 1.3.8 and Adblock Plus Pop-up Addon 0.2.5 both run on Firefos 4.1, but neither stops the peel back.
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