diff --git a/headlessDetect.js b/headlessDetect.js
index 6fddc9b..8de1d38 100644
--- a/headlessDetect.js
+++ b/headlessDetect.js
@@ -69,7 +69,10 @@ class HeadlessDetect {
         }
     }
 
-
+    // Explicitly set width for Firefox MOZ_HEADLESS_WIDTH=999 firefox -headles URL
+    testMozHeadlesWidth() {
+      return screen.width === 999 ? 1 : 0;
+    }
 
     //* Main Functions *//
 
@@ -94,4 +97,6 @@ class HeadlessDetect {
 
         return score / testsRun;
     }
-}
\ No newline at end of file
+
+}
+