If you design websites across different platforms, then you need an editor that can keep up with you. Komodo Edit is not only cross platform but it's completely free to use.
Even though it's free, Komodo Edit doesn't skimp on features, and includes everything you'd expect, such as autocomplete, syntax coloring and syntax checking. Even better, it's a little like Firefox in that it supports extensions and plug-ins to extend it's capabilities.
This shouldn't come as a surprise though, because Komodo Edit is built on Mozilla code and the same licensing rules as Firefox. All of the extensions have been created by the Komodo community so, as with Firefox, you're spoiled for choice.
The overall benefits of Komodo Edit is it should enable you to write code faster and shorten the coding learning curve for those that are new to it. As with Firefox, the drawback to it is that if you overload it with add-ons, you may experience plug-in conflicts that result in crashes and actually slow down your programming.
If you're looking for a web editor designed in the same spirit as Firefox, then Komodo Edit is an excellent choice.