I found myself with 3 browsers installed briefly, so I decided to test the resources that they use. It's too bad I didn't think of it while I had Mozilla Firebird installed, I could have tested that also, anyway here is the link: Computer World
I'm not sure I understand your question, I installed all three browsers and ran them on my computer, listed are the resourses used by each of them,according to windows task manager, if you want to you can do the same thing yourself, as stated it may vary from computer to computer
You can't really compare the memory usage of IE with any of the other browsers, since IE is integrated into Windows. The memory usage shown in task manager for iexplore.exe will always be less than it actually is.
IE's rendering engine and GUI are a part of windows, where-as Opera and Mozilla both have their own.
Mozilla and Opera are also handle multiple pages instead of just the one that IE does.
Mozilla and Opera will always take more memory than IE.
OK, I'm no expert here, but explorer.exe is as I understand it part of Windows itself, and runs no matter what browser you use. BTW if you check the results you will see Opera actually used the least ammount of resouces, Netscape used the most.