BUG: Cannot watch directv.com in Firefox

Steps to reproduce:

1. Open Firefox.
   1. Note that directv.com/guide works in Chromium browsers -- just not Firefox!
2. Go to directv.com/guide
3. Pick something to watch (anything) and click on it.
4. You should get a modal with a blue Watch button.
   1. Make sure that the laptop icon has a green check mark to indicate that you are allowed to watch it.
   2. If not, go back and pick a different channel.
   3. Click the blue Watch button.
5. A new modal appears... click Watch Live.
   1. Note that sometimes it take several clicks for this to work.
6. Now you will be prompted to Install DIRECTV Player.
   1. You are also told that you will need to restart your browser after installation.
   2. Click the blue Install DIRECTV Player button.
   3. You are then prompted to download VideoGuard.13.0.exe.
7. Download and install VideoGuard.13.0.exe.
8. Close Firefox.
9. Repeat Steps 1-4 above.
   1. At this point, you should expect the video to work. VideoGuard is installed and Firefox has been restarted.
10. Click Watch Live.
    1. You are prompted to Install DIRECTV Player again! 🐞
    2. No matter how many times you repeat these steps, you can never get past the Install DIRECTV Player modal.
       1. Disabling all Firefox security features and add-ons does not fix it.
       2. Using Incognito mode doesn't fix it.
       3. Disabling your VPN doesn't fix it.