[7" Kindle Fire HD General] sonicanomaly:
Successful Root on 8.4.3 with latest KFFirstAide

Well, after much trial and error, I'm fairly certain what was standing in the way of my drivers installation was the fact that my computer is old and on its last leg. After several failed attempts to get things installed, here's how I managed to successfully root 8.4.3 using only Kindle Fire First Aide on Windows Vista.

I installed the newest version of KFFirstAide (found here: http://xdaforums.com/showthread.php?t=2096888 ) using the installation instructions in the first post of this thread. I used it to install the adb drivers. This was problematic the first time, so I uninstalled them and tried again; the only reason it was problematic the first time was my system hung. Again, it's not a very good system that I'm using.

When installing the drivers, I got the first installer, and clicked install on it. Then I received a driver installation wizard, and proceeded on it. The wizard said the drivers installed correctly, so I clicked finish. The original installer said that the installation was not successful and that they had to be installed manually. I clicked okay and returned to KFFirstAide. It said to plug my device in, but since it hung up the first time I tried that, I didn't this time and instead closed out of KFFirstAide using the appropriate menu options.

Afterward, I plugged my kindle into the computer. The automatic driver detection thing in the taskbar tray spent a long time recognizing my device as two things, and searching for a third driver. During this time, the autoplay options for Kindle (as a portable device/drive) kept popping up several times. I dismissed it each time. After a very long wait, I got an alert that in order to install the drivers I needed to restart my system. So I did. It took a long time to shut down; something called CCC.exe (no clue what that is) tossed up an error that it wouldn't close so the system was waiting on it. I left everything alone, and ended up on a "configuring updates" screen. It had three stages, didn't explain what it was, and demanded I not shut down my computer. This took several minutes, and my computer was slow to start up afterward, but eventually evened out... with the drivers successfully installed.

I checked to make sure the adb drivers were working and all was well in the device manager when I plugged my kindle back in. It still took a slightly longer than ideal amount of time to recognize it as an adb device, but it did work. Then it was onward to rooting.

For my Kindle Fire HD 8.9" with firmware 8.4.3 I used the second (preferred) option for rooting, as found in this newest version of KFFirstAide. I followed the prompts on screen, let it do its thing, and all was well. I did get a very sluggish system with no icons at one point. Superuser (I believe it may be SuperSU actually) seemed to have started itself; I did not have to initialize it and couldn't find where to do so anyway. The previous step had mentioned Root Checker, so I ran it instead. Got the Superuser request, granted it, and confirmed root. Simple as that.

When I pressed any key to continue on the KFFirstAide program, it rebooted my kindle again, and the sluggishness and missing icons were fixed. I'm now rooted, and aside from issues I ran into with my computer and its insistence upon making my life a living hell, it was an extremely easy process. I'd say it was low-stress, but that may be a misnomer as I've watched videos of the rooting process and read a lot about it so I knew to expect the sluggishness and not to panic thinking something had gone horribly wrong.