diff --git a/4.1-Extensions.md b/4.1-Extensions.md
index 4055925..fd99e05 100644
--- a/4.1-Extensions.md
+++ b/4.1-Extensions.md
@@ -18,3 +18,14 @@ Borrowed from [MozillaZine: Custom headers](http://kb.mozillazine.org/Custom_hea
 5. Set the `In-Reply-To:` ie `user_pref("mail.identity.id1.header.InReplyTo", "In-Reply-To: <31ff00c2-b7cb-4063-beeb-a0bdd424c3a7@example1.tld>");`
 6. Restart Thunderbird and send your email.
 7. Comment out the above set options in your `user.js` with `/* */`. Go back into about:config ie (Edit → Preferences → Advanced → General → Config Editor) and rightclick on the keys `mail.identity.id1.headers`, `mail.identity.id1.header.References` and `mail.identity.id1.header.InReplyTo` and click *Reset*. Do not set these values to anything else in a `user.js`, because it will interfere with Thunderbird's normal behavior when you click Reply on an email.
+
+### Installing extensions from AMO (ATN)
+
+To allow smooth extensions install from AMO (<https://addons.thunderbird.net/>) with `thunderbird user.js`, you'll need to :
+
+* re-enable JavaScript (9230, `javascript.enabled`) ;
+* re-enable mozAddonManager API (4503, `privacy.resistFingerprinting.block_mozAddonManager`) ;
+* disable RFP, at least for `addons.thunderbird.net` (4505, `privacy.resistFingerprinting.exemptedDomains`).
+
+If you are not configured this way, Thunderbird will download extensions as .XCF archives instead of properly processing them.  
+If don't miss AMO integration, you can always download extensions before opening them using `Add-ons and Themes > Manage Your Extensions (cog wheel) > Install Add-on From File...`.