The memory efficiency doesn't explain much to me. It's like complaining that linux is holding memory hostage in buffers/cache or that Chrome should lose points for its process model. The test surely doesn't tell the whole story; not to mention, I can't be bothered to worry about a couple 100M when I can get 160 of them for the price of dinner. For all I know, the chunking I experience with FF could very well be a relic of their process and/or memory model.
And security is just a smudge on the score? No thanks.