diff --git a/1.3-Implementation.md b/1.3-Implementation.md
index 15affe9..e08c8e8 100644
--- a/1.3-Implementation.md
+++ b/1.3-Implementation.md
@@ -34,7 +34,7 @@ You will need to make changes. Make sure to read about applying `overrides` on [
 
 - FPI is enabled (4001)
   * It is recommended that you clear (Ctrl-Shift-Del) everything (except passwords) when first enabling (or permanently disabling) this, so orphaned Origin Attribute data is cleared
-- RFP is enabled (4501) and webGL is disabled (4513)
+- RFP is enabled (4501) and webGL is disabled (4520)
    * :eyes: The **letterboxing pref** `4504` and is independent of `4501`. FYI: this is the pref that creates borders around your webpages: if you want dark borders, use the hidden pref `ui.systemUsesDarkTheme` = `1`
 
 :exclamation: QUITE IMPORTANT: Other preferences may cause site breakage, but nothing that can't be fixed. You won't "lose" anything...- it's not the end of the world.