The nice folks at SiteVista have released a great free product – CSSVista -that allows you to edit CSS and see the results in Firefox and IE at the same time. This has quickly overtaken Chris Pederick’s Web Developer Toolbar as my most-used CSS tool. It’s not without its quirks and it’s astonishingly basic (it’s v0.1 after all!). However, it can handle relative paths to images and still display them (something Web Developer Toolbar can’t do). You get a split screen view of IE and Firefox at the same time, and this gives you instant visual feedback as you ENGINE CSS.
SiteVista make their money from serving you the results of multiple browser CSS testing, so have a look at their paid-for service while you’re there. I’ll be subscribing to their blog to get news about v0.2