IE will always beat the competition in initial startup time because, unlike the competition, it's tightly integrated with the operating system, not "bolted on" afterwards. Parts of IE are already running for other Windows tasks even without opening it , even though you may not realise it.
The "sync" feature in Firefox does not work automatically since you have to enter a code for the other device you want to sync, a bit clunky if you ask me.
Google Chrome's "Sync" feature is much more user friendly and it's automatic once you've created a Google Account and signed in. I've tried all the web browsers out there and none of them beat Chrome for my purposes: https://www.google.com/intl/en/chrome/browser/
There are very few websites which don't look right or work right in either Firefox or Chrome. I think I've come across only two in the last 6 years, and believe me I'm on dozens of websites every day, including some corporate, online banking, my investments etc)
Website compatibility was actually much worse than that with the latest version of IE because many companies hadn't updated their websites to recognise it. Consequently, I frequently saw this "Your version of Internet Explorer is too old" !
That's all in the past anyway, I never use it. Too bad you can't purge it from Windows altogether, otherwise I would.
(I don't even need it for Windows Update because I never use that either).