Recently I have been thinking about extensions/add-ons on android Devices. I have read somewhere that extensions don't work on android chrome. Is it true? Secondly, how can I develop extensions for android firefox ?Does the extensions build using sdk-addon for desktop browser will work for android devices?
Yes: if you develop a Firefox add-on with the add-on SDK, it will work on the Firefox Android browser. Not all the APIs are supported, and you need to create a separate build of the add-on. See https://developer.mozilla.org/en-US/Add-ons/SDK/Tutorials/Mobile_development for the details.