I am new to developing Firefox Extension.
I planned to make something like a web annotator extension, and people can share the notes on different computer. I am thinking to put the notes on an external database, for example, use an external MySQL database.
Is it possible to do this in Addon SDK? Thank you in advance.
Typically how developers solve this is by exposing the mysql database to the web as a web service ( written for example in Node.js, python, php, or whatever you're most familiar with ) and saving & fetching data to and from that web service using http requests.
The the web service client part of this, you would use the request module:
https://addons.mozilla.org/en-US/developers/docs/sdk/latest/modules/sdk/request.html