IE has the tabs inside of the pages now.
Also instead of alt+tab use CTRL+tab for the tabs.
Firefox has some fun plugins and is easy to skin ect.
There is almost nothing left that firefox has that microsoft hasnt copied. This is a common strategy for microsoft to copy off of anything the competition has in order to drive them out of business to make it a microsoft only world. Anyone remember netscape? Microsoft is trying to replace google atm although for the first time ever they aren't able to smash a company to the ground by making whatever they sell for free.
That being said IE will always be much more vulnerable due to 95% of viruses made for it. If IE was allow user made plugins then it would be flood of malicous code and viruses being added into IE. With firefox.linux when a person finds a security hole they report it and it is quickly partched up. With ie/windows it is immediately explioted or at the very least theres no real motivation to report it or even look for the security hole in the first place.