diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 2e87ef5e6e..321299822c 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -4397,7 +4397,7 @@ pref("image.decode-immediately.enabled", false);
 pref("image.downscale-during-decode.enabled", true);
 
 // The default Accept header sent for images loaded over HTTP(S)
-pref("image.http.accept", "*/*");
+pref("image.http.accept", "image/webp,image/png,image/*;q=0.8,*/*;q=0.5");
 
 // The threshold for inferring that changes to an <img> element's |src|
 // attribute by JavaScript represent an animation, in milliseconds. If the |src|