The OS/2 line of Firefox ESR stopped at the Firefox V10.x ESR releases. In spring 2013 bitwiseworks planned to work on an ESR V17.x branch port for OS/2 and eCS. The port is a donation based project and not by surprise the release is still not out because not all of the required money has been yet collected. Now it happened that Mozilla already switched to the new ESR branch V24.x some days ago and that will make this still unfinished port already an old version. For more check the Mozilla ESR for OS/2 project page at https://github.com/bitwiseworks/mozilla-os2 .
Update 10/22/2013: The developer could build a test build that can be seen in the screenshot. An official puplic build should be available within the next few weeks.