You can download the update directly on your device through the Google Play Store or by using the following link:
Firefox for Android version 20.0 has the following new features and improvements:
- Per-Tab private browsing
- Gingerbread and Honeycomb support for H.264/AAC/MP3 hardware decoding
- Top Sites in about:home is now customizable
- The 'Quit' menu item has been removed from Firefox versions running on ICS and higher. When done browsing just tap swipe off recent application list. Use the QuitNow add-on if you want more control
- System requirements have been lowered to 384MB of RAM and QVGA displays