I’m still looking for a Firefox extension that will turn any textarea (such as those found in forms) into a powerful text editor. Meanwhile, I just found Xinha Here! It turns any textarea into a pretty decent HTML editor. The little secret is that an HTML editor is also a text editor. Not a very powerful text editor, but you have search and replace!
In a day and age when I start wondering whether my kids will not learn about programming in a browser, a good browser-based text editor is really needed. We need more tools like Xinha.