I just told Jeremy that someday I might list off my current FireFox plugins, and I guess today is just as good as any other. So here they are:

• Gmail Notifier - If you have Gmail and your own Windows account, it automatically checks how much Gmail you have. I have mine set so that when I click on the Gmail icon in my FireFox statusbar, it opens my Gmail (already logged in) in another tab.
• FoxyTunes - If you listen to music on your computer, like I do during every minute I'm on my computer, then you need FoxyTunes. It'll take the song information and give you player controls for your favorite music player right in your statusbar. I usually have my iTunes minimized to the Windows Taskbar, so the player controls are there, but it's great to have a display of what song is playing scrolling right above the controls while browsing.
• IE Tab - That's right, don't open that pesky Internet Explorer ever again. While browsing with this plugin, you can right-click on any link and it select to "Open in IE Tab" which is a FireFox tab running Internet Explorer. Also, at any time, click the FireFox logo to toggle the current page to IE vieweing. Great for seeing how your website will look in the competitor's browser.
• Web Developer Toolbar - If you work on websites at all (like I do), then you definitely need this one. It gives you a whole toolbar to debug websites with. You can easily disable JavaScript, disable CSS, and much, much more. Some of my favorites are the CSS it uses to display the class and ID names or the outlines of every block-level element. It's a lifesaver for figuring out the pesky CSS spacing problems (and much more).
• HTML Validator - If you make websites (again), you need this. It validates your page and shows you if it passed or not right on your statusbar. It also gives the validation errors right in the "View Source" window too. Great stuff.
• ColorZilla - Need a color palette but don't want to open PhotoShop? Want to get that color right off the page? No more need to take a screenshot, this little utility in the bottom left corner of your FireFox window is a full-featured color picker. Click on it and then anywhere on the webpage to pull the color. Double-click on it to get a full, PhotoShop-style picker.
• MeasureIt - This one may not be needed because the Web Developer Toolbar (mentioned above) has a ruler built in the latest version, but this one is more handy. That is, it sits in the bottom-left of your browser window and is activated with just one click. Select a square of web page real estate and find find out how many pixels it occupies.

So there you have it. Use these powers well and use them wisely. And if you have some extension you think I really need to check out, put it in the comments.