This would save enormous amounts of time, as Firebug is what I use to debug anyways.
I would just like to save the changes I’ve made to a remote or even local directory. Is this possible?
(bonus: can I do php development also, and not just html/javascript/css?)
You can save the changes you made in Firebug for CSS and HTML by just copying it and pasting in your editor of choice. However inside Firebug itself there is no function for saving the contents that I am aware of.
I second the Web Developer extension. It is amazing tool for writing CSS and HTML, as you can see the changes you make for CSS and HTML right in front of your eyes. Web Developer is almost an editor on its own built into the browser.
For PHP debugging with Firebug check out the FirePHP extension.