The point is that you've presented memory usage in an entirely useless and misleading way. You've identified that firefox uses lots of memory. Congratulations. Did you try to account for this memory usage? Nope.
It doesn't take much effort to realize that FireFox's increased memory footprint is mostly a result of a more aggressive caching policy. And that the cache has a fixed size (see: "about: cache" in FF). If you really want, I believe you can cut down on that memory usage. Although, I don't know why you're worried about less than 64 MB of memory on a modern system.
Take the fixed-cost cache out of the equation and you'll see that FireFox and IE have similar per-page memory usage. Your presentation masks this fact. Rather than reporting the memory usage with 8 tabs in FireFox, you just say "if i had 8 open pages like I did with IE (or 8 tabs) i shudder to think what the memory consumption would have been". In case you were wondering, it'll be about the same as IE plus the cache size.
I guess it's up to you whether or not you think having correct HTML is important. It'd be fairly trivial to make your site compliant. Nonetheless, your implication that FireFox has an inferior rendering engine is questionable at best. If given the opportunity to drop support for either IE or FireFox, I think most web developers would pick IE.
I don't know if this is your site (), but it doesn't display correctly on FireFox. The red box and text for the right menu is all messed up. It looks like the site relies on a fixed size font. Which is a design no-no. The Oxacah site also deforms poorly with large text, but it does remain readable.
