Mac users who have recently upgraded Firefox or Thunderbird to version 10 may have noticed that Control+Option+V, the shortcut key prefix for inserting a clipping using the keyboard, no longer works.
If this is happening to you, there is a workaround available:
Download and install the Keyconfig extension (also available here). After installation, look for the menu item under Tools -> Keyconfig, or open the preferences dialog for this extension from Tools -> Add-ons.
Locate the command named Insert Clipping. This is the command that is called to insert a clipping using the keyboard.
Select the existing shortcut key and change it by pressing a new shortcut key combination on your keyboard (for example, Command+Option+V), then click Apply. You can then use this shortcut key combination to paste a clipping using the keyboard.