Thanks to everyone who participated in the poll last week!
In a perfect world, we wouldn't need things like the IE View Add-on for Firefox. Every website would display equally well in every browser, in a perfect world -- you'd never see messages saying "This website requires [a different browser than the one you are using]," and website developers would only need to test their pages in one browser, since they would all work equally well.
But it's not a perfect world. Some websites still only work in Internet Explorer (for example, the Windows Update website), and creating brand new web pages involves tedious cross-browser testing in both Firefox and Internet Explorer (not to mention Safari, and Opera, and Lynx...). In our imperfect world, IE View is a big help for web developers and anyone who dreads those tiresome "This website requires Internet Explorer" messages.
What it's good for: IE View takes you from viewing a web page in Firefox to viewing the same page in a new Internet Explorer window, in just one step (as opposed to copying the URL from the Firefox address bar, opening Internet Explorer manually, waiting for the default IE homepage to load, pasting in the URL, and then waiting for that to load too).
How it works: Once you have IE View installed (see instructions for how to install Firefox Add-ons), right-click on a web page. Select the menu option to "View This Page in IE" and an Internet Explorer window will open with the same web page.
IE View also creates an option in Firefox's Tools menu to "Always View This Page in IE," for frequently-visited pages that don't play nicely with Firefox.
Have a favorite Firefox Add-on? Let us know what it is in the comments!