diff --git a/modules/programs/firefox/mkFirefoxModule.nix b/modules/programs/firefox/mkFirefoxModule.nix
index e2e9935c7..74639dc76 100644
--- a/modules/programs/firefox/mkFirefoxModule.nix
+++ b/modules/programs/firefox/mkFirefoxModule.nix
@@ -874,7 +874,11 @@ in
                 "chrome"
               else
                 "chrome/userChrome.css";
-            sourcePath = if lib.types.path.check profile.userChrome then profile.userChrome else null;
+            sourcePath =
+              if ((i: lib.isPath i && lib.types.path.check i) profile.userChrome) then
+                profile.userChrome
+              else
+                null;
           in
           # Merge the regular profile settings with extension settings
           mkMerge (
diff --git a/tests/modules/programs/firefox/profiles/userchrome/chrome/userChrome.css b/tests/modules/programs/firefox/profiles/userchrome/chrome/userChrome.css
index 120791fd7..bc84d62bd 100644
--- a/tests/modules/programs/firefox/profiles/userchrome/chrome/userChrome.css
+++ b/tests/modules/programs/firefox/profiles/userchrome/chrome/userChrome.css
@@ -1,3 +1,7 @@
+/*
+  This is a simple comment that should be written inside the `chrome/userChrome.css`
+*/
+
 #urlbar {
   min-width: none !important;
   border: none !important;
diff --git a/tests/modules/programs/firefox/profiles/userchrome/default.nix b/tests/modules/programs/firefox/profiles/userchrome/default.nix
index a0640afd8..a174f3ce4 100644
--- a/tests/modules/programs/firefox/profiles/userchrome/default.nix
+++ b/tests/modules/programs/firefox/profiles/userchrome/default.nix
@@ -18,14 +18,17 @@ in
         basic.isDefault = true;
         lines = {
           id = 1;
-          userChrome = # CSS
-            ''
-              #urlbar {
-                min-width: none !important;
-                border: none !important;
-                outline: none !important;
-              }
-            '';
+          userChrome = ''
+            /*
+              This is a simple comment that should be written inside the `chrome/userChrome.css`
+            */
+
+            #urlbar {
+              min-width: none !important;
+              border: none !important;
+              outline: none !important;
+            }
+          '';
         };
         path = {
           id = 2;
diff --git a/tests/modules/programs/firefox/profiles/userchrome/expected-userchrome.css b/tests/modules/programs/firefox/profiles/userchrome/expected-userchrome.css
index 120791fd7..bc84d62bd 100644
--- a/tests/modules/programs/firefox/profiles/userchrome/expected-userchrome.css
+++ b/tests/modules/programs/firefox/profiles/userchrome/expected-userchrome.css
@@ -1,3 +1,7 @@
+/*
+  This is a simple comment that should be written inside the `chrome/userChrome.css`
+*/
+
 #urlbar {
   min-width: none !important;
   border: none !important;