VERY EARLY DOWNGRADE GUIDE (USE AT OWN RISK)

This method has been tested on O3DSXL 9.9.0U with Menuhax 2.1. Remember to always use latest hax builds, old hax builds are more likely to fail.

You will need:
1. 9.2.0 update files according to your region and console version. Examples: 9.2.0-20U(Full).zip for USA O3DS, 9.2.0-20E(Full)_n3ds.zip for EU N3DS.
Get 'em from 3DSISO. http://www.3dsiso.com/cia-format-dlc-s-themes-and-updates/268700-mega-cia-bin-mset-4-6-backups-browser-backups-update-packs-regions.html?highlight=firmware
2. Bricktool tester and Bricktool. https://mega.nz/#!tAtEDKhC!vAFHGKtpccdjg3f2MLu0TIBtriFDif_tBjanujchWGw
3. An O3DS/N3DS/2DS with <=10.3 firmware (at time of writing), running homebrew with your preferred entrypoint (Menuhax or Ironhax). XL versions also included, obviously.

Steps:
1. Copy the "updates" folder with all the CIA files in it to your SD card.
2. Copy the bricktool tester and bricktool into your "3ds" folder.
3. Boot up homebrew and run the bricktool tester. It should look like this. http://i.imgur.com/XCWVDup.jpg Abort if it doesn't look like this.
4. Reboot your console, boot up homebrew, and run the bricktool (which is sysupdater, I just wanted to be funny). Hit Y and watch your system downgrade.
5. If you're using Menuhax (likely), kill your console with the power button and remove the SD card. Go into the Nintendo 3DS folder and find the extdata folder to delete it. This removes Menuhax.
6. Go back in, and set up Browserhax again, and set up CFW as per normal.

Credit goes to the relevant people. Shinybanana, AlbinoDrought, profi200, smealum, plutoo, yellows8, Steveice10, 3dsguy/ps3hen... whoever else I missed. Fuck it, go enjoy your piracy.