If you do any amount of web development, professionally or personally, then you should definitely be using these:

Firefox

This is simply the best browser out there. Both in terms of it’s W3C compliance and the many add-in’s available. It took me awhile to learn this as I was stuck in corporate America where Internet Explorer is used simply because it is already installed. This said, even if you become a convert, if you do any web development where you are customizing the graphical presentation of your content, then you owe it to the folks you are trying to reach to always test your output in a variety of browsers and versions. Wondering what these would be? Well, visit W3 Schools to find out. Keep in mind, however, that the statistics presented are based upon fellow developer and web technologist browser utilizations and may not be representative of general or corporate use.

Developer Toolbar

Okay, now that you have installed and are using Firefox, it is time to get the one toolbar you will never be able to do without. It is the Web Developer Toolbar. Whether you are a seasoned professional web designer, someone just learning or just enjoy web development as a sideline, this toolbar is a “must have” tool. It will take awhile to check out the many features but I whole heartedly suggest you nose around. From turning off all style sheets to see what the “empty canvas” actually looks like (CSS>Disable Styles), to outlining various page elements, to displaying rulers, you won’t be disappointed with all the useful features. In fact, you’ll wonder how you ever got along without it.