Personally, when I did loads of HTML and JS for blogs, I had IE (since it was un-removable), Firefox and Opera. Just so I could test in each browser.But now I'm on Linux, which actually comes with Firefox 2... not really pre-installed, but you can choose to install it when you install the OS.But I don't do much HTML and JS. Not recently anyway.I think, with serious web development, you should test on a few different browsers. And probably a few different versions, to account for older versions.Which can be a problem, since it means having a load of browsers on your computer.Firefox 2 is my favourite browsers, though. Decent debugging console thing. Wonderful amount of themes and add-ons.I think the fact that it's open-source, too, it what makes it better.Updates and improvements can be made as and when they need to be. So you can always get a decent stable version. Whereas IE either installs separate updates, and then puts them into the next release, which takes a while to come around.Not to mention that given Firefox's open-source nature, finding and exploiting security holes is more of an issue, so more attention is paid to making it more secure, I would think.IE is closed, so security holes aren't found until after they've been exploited, and then MS releases updates and patches. I'm not absolutely certain about that, but it seems like that's what makes Firefox more stable and secure.