diff --git a/webextensions/manifest/theme.json b/webextensions/manifest/theme.json
index 5da02340b7dd8c..fff0334dee9794 100644
--- a/webextensions/manifest/theme.json
+++ b/webextensions/manifest/theme.json
@@ -918,7 +918,8 @@
                 },
                 "edge": "mirror",
                 "firefox": {
-                  "version_added": "55"
+                  "version_added": "55",
+                  "notes": "CSS gradients are supported from Firefox 153."
                 },
                 "firefox_android": {
                   "version_added": false
@@ -939,7 +940,8 @@
                 },
                 "edge": "mirror",
                 "firefox": {
-                  "version_added": "55"
+                  "version_added": "55",
+                  "notes": "CSS gradients are supported from Firefox 153."
                 },
                 "firefox_android": {
                   "version_added": false
@@ -978,6 +980,27 @@
               "safari_ios": "mirror"
             }
           },
+          "additional_backgrounds_size": {
+            "__compat": {
+              "support": {
+                "chrome": {
+                  "version_added": false
+                },
+                "edge": "mirror",
+                "firefox": {
+                  "version_added": "153"
+                },
+                "firefox_android": {
+                  "version_added": false
+                },
+                "opera": "mirror",
+                "safari": {
+                  "version_added": false
+                },
+                "safari_ios": "mirror"
+              }
+            }
+          },
           "color_scheme": {
             "__compat": {
               "support": {