Where Internet Explorer is more secure than Firefox

Instead of warning you about password-containing URLs, Internet Explorer prevents you from loading such URLs at all and displays a URL syntax error.

Internet Explorer warns you when adding a bookmarklet. The dialog says "You are adding a link that may not be safe. Do you want to continue?"

Internet Explorer requires software installed using ActiveX to be signed. While this does not deter spyware makers, who sign their software, it does deter casual malicious software authors.

Where Firefox is more secure than Internet Explorer

Internet Explorer is vulnerable to an attack that allows software to be installed without your permission. The attack involves getting you to click on particular part of the page or type a word containing 'Y'. The page then pops up an ActiveX software installation dialog as you are about to click or type the key. This was fixed in bug 162020 for Firefox.

If you use Internet Explorer, sites can read the contents of your clipboard directly. Before going to untrusted sites, clear your clipboard, and avoid leaving passwords on your clipboard in general.

If you use Internet Explorer, web pages you have open can change the content of your clipboard at any time. If you paste into any program (even immediately after copying text from the same program), the web page can control what you paste. In certain programs, such as a DOS prompt or IRC program, pasting text containing line breaks causes commands in that text to be executed, giving the attacker control over your computer. Thus, you should never paste into a DOS promopt or IRC program while viewing an untrusted web page in Internet Explorer.

We believe that Firefox's software installation dialog is more clear than Internet Explorer's, which is important for new users but not as important for advanced users.

Other differences

To see Google PageRank in IE, install the Google Toolbar. While you can't make this toolbar show PageRank and nothing else, you can put it to the right of the menu bar to save vertical space.