Firefox has pretty much replaced Safari, AOL, and… really, just about every other web browser in existence. It has become as standard an internet interface as Microsoft Windows has become for PC operating systems. So in putting together this list of great internet browser extensions for web designers, we figured “Why focus on anything besides Firefox?”

So here you go, seven really cool, totally free, Firefox extensions that you really ought to take for a spin if you design websites for a living…

Internet Explorer Tab

We may have said that Firefox is clearly winning the race for hottest web browser, but a lot of people are still using IE. This means that your site designs need to be compatible in both browsers. Well, instead of keeping IE and Firefox windows open just to check for compatibility, IE Tab lets you check IE compatibility right in Firefox. Cool, right?

Ad Sense Preview

Maybe one of the most useful tools out there if you’re hoping to make a dime or two on Google Ad Sense revenue. You get to take a look, in preview mode, what ads are going to be placed on your site without the hassle of setting up a new adsense account. Incredibly convenient little extension.

Server Switcher

This one lets you switch between your live and development server with the click of an icon. Incredibly useful for going back and forth for reference.

Codetech

Like Dreamweaver but don’t want to fork over a few hundred bucks for it? Check out Codetech, a Firefox embedded page editor with the feel of Dreamweaver, but without the massive pricetag.

SEO for Firefox

Here’s another great one if you’re hoping to make some cash on ads. This handy plug-in lets you check useful market research data including Google PR, Age, Alexa rank, etcetera etcetera, right in the browser while looking at your site.

Screen grab

Not the most exciting add-on on the list, but a necessity nonetheless. Just as you might guess, Screen grab lets you take, well, screen grabs of the sites you’re working on, saving you the time of copying the whole screenshot into Photoshop for cropping. Just click, and there you go, you got yourself an image of your work to submit to CSS galleries or clients for a WIP preview.

Server Spy

Ever want to scope out the competition? Server Spy lets you check out what brand of HTTP server any site is running on, displaying it right there on the lower right corner of the browser. Just a handy little tool to skip some guesswork.

Gil Smith writes about how to apply to web design colleges.