I want to help translate Fx extension into my language but i noticed that Fx does not use .po files. It is using dtd files. Is there a program to help me translate these kind of files?
The translation process for Firefox extensions is managed at http://www.babelzilla.org/ - chances are you can find the extension you are trying to translate there.
There are tutorials on how to use the web-based translation service at http://www.babelzilla.org/index.php?option=com_content&task=view&id=13&Itemid=220