Filed under, “not sure if I need it – but thanks, just in case” we have Texto.  This add-on for Firefox will allow you to launch an external text editor to edit text forms in Firefox. 
Here is a little more about the add-on from the Texto developer:
This add-on strips out much of the Mozex functionality to focus on launching external text editors. Features the ability to customize editor behavior for different websites, and uses the asynchronous process support [...]

You can drag your tabs around and organize them like you want to have them by default. There is no doubt this is one of the more useful features Firefox has put in the browser in some time. What about grouping your tabs by the source? You can’t do that until you pick up the Separate Tabs extension for Firefox.
+ Download and Install the Separate Tabs Extension for Firefox!

Need a few more handy extras with your Firefox install? Well instead of finding a lot of tiny extensions to do your tasks, why not give the Handy Xtra Stuff extension a shot?
Adds some handy extra toolbar and other functionality to Firefox, including: Custom webpage source viewer button + configuration dialog, Toggle online/offline button, Tabbar customization UI, Copy ALT/TITLE text menu options, Popup ALT text option.
+ Download and Install the Handy Xtra Stuff Extension for Firefox!

Reading the source code from a Web site can be really confusing if you don’t know what you are looking at. Thankfully for those of us who get mixed up with all the code with no fluff, there is the View Rendered Source Chart extension for Firefox.
It allows you to view the source of a Web site with color coded boxes around all the important parts. It might sound a little silly, but it is a great way [...]