How to make Mutter default window manager I'm running Debian Squeeze and removed Metacity in favor of Mutter. How do I avoid having to run `mutter --replace` each time I start Xorg (GNOME)?

Press Alt + F2 and enter `gconf-editor`. Navigate the tree menu to desktop > gnome > session > required-components. Now, replace the `windowmanager` key with the window manager of your choice. Just replace gnome-wm (or metacity) with mutter.

Another possible solution:

You could add `mutter --replace` to **System** > **Preferences** > **Startup Applications** which opens **`gnome-session-properties`** program:

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