i3: don't use a layout for something that simple

New windows are not created as tabbed but follow the default layout of
the workspace. So, set this default and just run firefox from there.

config

@@ -167,6 +167,6 @@ for_window [class="Spotify"] move to workspace number 3
 exec_always --no-startup-id exec systemctl --user start --no-block i3-session.target
 exec --no-startup-id exec i3-msg "\
   workspace number 1; append_layout ~/.config/i3/ws-emacs.json; exec exec emacs; exec exec $term; exec exec $term; \
-  workspace number 2; append_layout ~/.config/i3/ws-firefox.json; exec exec firefox; \
+  workspace number 2; workspace_layout tabbed; exec exec firefox; \
   workspace number 3; exec exec $mediaplayer; \
   workspace number 1"

ws-firefox.json

@@ -1,7 +0,0 @@
-{
-    "layout": "tabbed",
-    "percent": 1,
-    "nodes": [
-        {"swallows": [{"class": "^Firefox$"}]}
-    ]
-}