Is it possible to modify/edit, already installed firefox addons? Where are the addons stored in the computer... I mean which folder etc...
It is possible to edit the files. Its simple to find the folder path.
you should find all the extension files in here. Your extension could be a .xpi file which is nothing but a zip file. copy it to a different folder and rename it to .zip. Unzip it and browse the content in it. Hope this helps.