diff --git a/mousetrap.js b/mousetrap.js
index 6e281461..2ec6b6f9 100644
--- a/mousetrap.js
+++ b/mousetrap.js
@@ -88,6 +88,15 @@
         222: '\''
     };
 
+    /**
+     * Firefox's API "InstallTrigger" to install add-ons is unique to the browser.
+     * This is to resolve issues in https://github.com/ccampbell/mousetrap/pull/215/
+     */
+    var isFirefox = typeof InstallTrigger !== 'undefined';
+    if (isFirefox) {
+        _KEYCODE_MAP[173] = '-'; // FF keyCode for '-'
+    }
+
     /**
      * this is a mapping of keys that require shift on a US keypad
      * back to the non shift equivelents