Memory. Footprint. Exists.
That phrase doesn't mean what you think it means.
"Memory Footprint" simply means the amount of RAM consumed by an application. It exists for every single application ever and that will be written in the history and future of computing. Some are larger than others.
What matters is *how that memory is utilised*. Does the memory usage improve the user experience? Are there memory leaks, or does memory get effectively reused?
FSO uses a *lot* more RAM than Freespace 2 did - but FSO is most definitely better than the original. Thus the memory usage is an improvement.
Firefox caches to RAM to have faster browsing.
IE caches to the hard disk instead. (Have a look in Temporary Internet Files.)
Thus IE is slower to use, while Firefox is much faster but will have increasing memory usage over time until it reaches the self-imposed ceiling.
It is possible to disable the memory cache in about:config, but it's not recommended because it slows Firefox down.
If you want a browser with a tiny memory footprint, then try Lynx. You won't like it though.
So, what's the 'killer feature' that you like in IE?
I haven't found
anything that's best in IE, except that IE6 properly displays pages designed for the IE6 abomination of HTML.
There are things that Opera does better and things that Firefox does better. I've not tried Chrome yet (and probably won't for a few years) so can't comment on that one.
None are perfect however - there is definitely room for improvement in both browsers.