Apologies, I definitely misremembered the facts and should have checked up on it.

I wonder how many iframes the average page has though, especially given Facebook like buttons and similar widgets. And someone like me, who maintains hundreds of tabs, could easily take up a few gigabytes of memory per addon, even if the amount of memory used for a single frame isn't that high.

I'm sure ABP was not the cause for the entire amount of memory in this case (or perhaps not at all), but many addons, each adding a bit of weight, can add up quickly.