add firefox no tab instructions

firefox/README.md

@@ -0,0 +1,3 @@
+toolkit.legacyUserProfileCustomizations.stylesheets to true
+
+cp <profile>/chrome/userChrome.css

firefox/userChrome.css

@@ -0,0 +1,10 @@
+/* hides the native tabs */
+#TabsToolbar {
+  visibility: collapse;
+}
+#titlebar {
+  visibility: collapse;
+}
+#sidebar-header {
+  visibility: collapse !important;
+}