There are definitely caveats with having this particular build of Ice Cream Sandwich on the Kindle Fire:

1. Native Video Player app is finicky. My solution? Stay away from using it and use MoboPlayer instead.
2. Netflix doesn’t work. I’m hoping an update will fix this.
3. Chrome Beta is buggy. I mean, it is in beta. The app runs but certain drawing elements that make up the app, i.e. tabs, won’t display. Enter Dolphin Browser® HD. The built-in browser that came with ICS is not too shabby either.
4. Kindle Fire doesn’t have a Camera, Bluetooth controller or a GPS. But you already knew that.

These are the main caveats that I consider deal-breakers. Consider reviewing this list of compatible apps that works with CyanogenMod9/Ice Cream Sandwich before installing.

On with the steps!

1. Download USBWOOT.zip and gapps-ics-20120207-signed.zip. USBWOOT.zip contains files that we need to flash the Kindle Fire with ICS. gapps-ics-20120207-signed.zip contains files that we need to install Google Apps like Market, Talk, YouTube, etc. Be sure to not extract the zip files.
2. Connect your Kindle Fire to a PC (or Mac). Transfer the files that were downloaded from the previous step. Safely eject the Kindle Fire to disconnect it from the PC. once you’re done and then turn off the Kindle Fire.
3. Turn on the Kindle Fire to boot. You should see a yellow triangle with a fire on it. Quickly press and hold the the power button. The power light should change from green to amber. Once the amber light goes away, release the power button.This should enter the Kindle Fire in recovery mode.
4. Perform a backup of the contents of the Kindle Fire. If you decide later down the line that ICS is not for you, you can revert back to its previous state. Tap Backup > Backup Now. As soon as the backup is done, go back to the main screen by tapping the home icon on the upper right.
5. Tap Wipe > Factory Reset > Factory Reset! to confirm. As soon as the wipe operation is done, go back to the main screen.
6. Tap Install. Select the USBWOOT.zip file on the right portion of the screen and tap Flash. Allow the flash operation to complete.
7. Repeat the same process above but with a different file. Select the gapps-ics-20120207-signed.zip file to install Google Apps. Again, allow the flash operation to complete.
8. Go back to the main screen. Tap on Wipe > Dalvik Cache > Wipe dalvik-cache! to confirm. As soon as the wipe operation is done, go back to the main screen.
9. Tap Reboot. You should see the Ice Cream Sandwich boot animation. Enjoy your Kindle Fire with Ice Cream Sandwich!

I hope you found the steps straightforward! I didn’t go into great detail about how you can recover from a backup. I haven’t done it myself but I can imagine it’s similar to the installation process. If there’s anything that’s not clear about them, please let me know in the comments section.

I’ve included a few screenshots of how Ice Cream Sandwich turned out on my Kindle Fire.

You’ll need the Android SDK, Java Development Kit in order to root your Kindle Fire with these steps. The SDK and the JDK downloads may vary depending on your machine. I won’t go into great details about installing the Android SDK and the JDK because it’s pretty self-explanatory. Here goes:

1. Assuming that you have the Android SDK installed already, open the file below in Notepad or a text editor of your choice.

   C:\Users\Your_User_Account\.android\adb_usb.ini

2. Edit the file and type in 0×1949 (Zero, not O) at the last line of the file. It should look like the screen below.Note: I created a new line for each #/comment to make it easier to read.
3. Navigate to where you have the Android SDK installed. It may be in your Program Files or Program Files (x86) directory. I have mine installed on the D:\ drive. With the example shown below, open the file below in Notepad or a text editor of your choice.

   D:\Android\android-sdk\extras\google\usb_driver\android_winusb.inf

4. Insert the following strings in a new line after [Google.NTx86] and [Google.NTamd64]. There should be two instances.

   ;Kindle Fire
   %SingleAdbInterface% = USB_Install, USB\VID_1949&PID_0006
   %CompositeAdbInterface% = USB_Install, USB\VID_1949&PID_0006&MI_01

   Save the file after you’re done.

5. Plug in your Kindle Fire to your computer using a micro-USB to USB cable. Windows will attempt to install the USB drivers for your Kindle Fire. Whether it succeeds or fails from installing the drivers, we’ll load the drivers that we’ve prepared from Step 4.
6. Open Device Manager. I use a keyboard shortcut to get to the Device Manager: Windows + Pause Break key. Then click on the Device Manager on the left hand side. Select the Kindle device  in the Device Manager tree and right click to bring up Properties.
7. Update the driver by selecting the modified android_winusb.inf file from Steps 3 and 4. You’ll get a warning that it may not be safe to install the drivers but we’re going to install it anyway. Click through the prompts to finish updating the driver.
8. Open the command prompt. I’m partial to using keyboard shortcuts so I would press the Windows + R keys and type in:

   cmd

   and then hit Enter. We’ll need to change to the directory of where the Android SDK is installed. On my machine, it’s installed on the D:\ drive so for illustrative purposes:

   cd D:\Android\android-sdk\platform-tools\

   Run the following commands. Press the Enter key after each one.

   adb kill-server

   adb devices

   We’re almost there! If you see your device listed after the previous command, that means you’ve been following every step. Make sure that you see your device listed before proceeding.

9. Download the Kindle Utility Fire. Save this on your Desktop or Downloads folder. Extract its contents.
10. After unzipping the file from the previous step, ensure that your Kindle Fire is still connected to your machine. Run the run.bat file.
11. You should see the following screen:You can choose to install the BurritoRoot (2), which is temporary or opt to permanently root (3). You’ll just need to follow the prompts/ignore some errors. The last thing you’ll need to do is to press any key to complete the process.
12. That’s it! Your Kindle Fire should now be rooted!
13. Bonus step: If you want to install Ice Cream Sandwich (or any other custom ROM), make or restore from a backup on your Kindle Fire, you’ll definitely want to Install latest TWRP Recovery (selection #5).