I have built and ported Firefox OS 3.0.0-prerelease (later renumbered 2.5) for ZTE Open.
This is an unofficial build. You may brick your phone and/or loose your data. I disclaim all responsibility of the resulting consequences. Flashing this build will void your warranty.
Features:
-Production build,
-Original boot animation.
What doesn't work:
-FM radio only works with speakers,
-Home light,
-Video recording.
Other things may not work.
To update, you must have CWM recovery installed (if not, see this link).
Instructions:
1. Backup your data.
2. Download the zip update here.
3. Copy the update zip file to your SD card and rename it update.zip.
4. Boot your phone in recovery mode (hold volume up and power buttons).
5. Select "install zip" and "apply /sdcard/update.zip" (this may take a few minutes).
6. Reboot your phone.