Hey, I'm making firefox extension, that will be simple html editor,
this is a site: http://code.google.com/p/intabeditor/

Its going to be not WSWIG html editor, but rather mini-notepad, so its
simple to do. I have got a bit of code now, and its almost working. So
im waiting for someone who want to help

When I was learning HTML, i was thinking 'does it exist an extension
for firefox, that allow me to have an text editor in a tab, so I dont
need to change windows from firefox to text editor, everytime when i
want to make changes to my page. Its so simple to write a code and
check results in the same window.

Its almost done. This is how does it work:
When you open a page from your hard disk, in address bar there will be
small 'pencil' icon. When you press it, a new tab with source of the
page will be opened. You can now edit this source. To save changes
just click save icon, that is on address bar.

Regards, Ireko