I have just finished developing the initial version of the Turkish Deasciifier add-on for Firefox. You can see the add-on at https://addons.mozilla.org/en-US/firefox/addon/204311/. I’ve prepared it using Jetpack SDK and the source code is available at http://github.com/emres/jetpack-turkish-deasciifier.
The add-on is still not reviewed by Mozilla team, I plan to apply for review after some users try it and use it without any problems.
For everything related to this add-on and its Python implementation read my blog entries at http://ileriseviye.org/blog/?tag=turkish-deasciifier