Mostly Smooth Upgrades
When you install the new IE (a roughly 15MB download), you'll be prompted to check for updates and then run Microsoft's malicious-software removal tool, which scans for viruses. The first time you launch IE 7, you'll also see a new page asking you to choose a default search engine and whether to run the antiphishing guard.
The new IE will save your old bookmarks and some settings, including your chosen privacy level for handling cookies. Other items may be reset. In my informal test, IE 7 reset my custom security configurations for the Internet zone to the Medium High default setting; if your security is set to High, however, IE 7 will preserve it.
Microsoft also says that IE 7 won't try to change your default browser if your choice is not IE, and that it should use roughly the same system resources as version 6.
The Firefox 2 download is a much smaller 5MB, and also seems to use fewer resources than IE 7. In my informal tests immediately after installing and launching IE 7, the browser with three open tabs used 80MB of memory; under similar conditions and with the same three tabs, Firefox used 58MB. Otherwise, the performance of the two browsers appeared similar.
When you install Firefox, you'll see a pop-up prompt to check for updates to themes and extensions you have that aren't yet compatible with the new version. Popular extensions typically update quickly; other add-ons and many themes can take weeks longer. If you have incompatible add-ons, the browser upgrade will still occur, but those add-ons will be disabled in version 2 until updated extensions are available (check by clicking the Find Updates button in the add-ons manager).
Firefox preserved my bookmarks and most of my test settings from version 1.5, including my master password for saved log-ins and my chosen default font. The cookie setting didn't transfer because my particular choice (to allow sites to set cookies unless I have removed their cookies in the past) isn't the same in Firefox 2. You'll find some settings in different areas of the Options window, also; for example, password preferences are now under Security instead of Privacy.
Let the Wars Rage
IE 7 includes other new features, such as quick page zooms and enhanced Web page programming support. Such tweaks, combined with the browser's major improvements, might slow or even halt the generally steady IE-user flight toward Firefox.
But it's telling that the last time we compared the major browsers, back in January, we looked at beta versions of Firefox 1.5, IE 7, and Opera 9. Mozilla will effectively lap Microsoft by releasing both 1.5 and 2 in the time Microsoft took to complete IE 7. (Opera remains at version 9.)
Which one should you use? For satisfied Firefox 1.5 users, moving to version 2 is a no-brainer, as they'll get new features and won't be thrown off by major interface changes. Confirmed IE users have a similarly easy choice: IE 7's features make it a much better browser than 6.x, and its security enhancements alone make it a must-have.
Of the two rivals, Firefox remains the better application. Since IE users will have to adjust to a new layout and interface anyway, this might be a good time to give Firefox a try, then watch IE 8 play catch-up again in five years.