Many Clippings users have asked for a different prefix shortcut key combination, replacing the current CTRL+ALT+V prefix (Mac users need to hold down the Control and Option keys while pressing V), to trigger keyboard insert.
There is an extension for Firefox and Thunderbird, Keyconfig, that lets you change shortcut keys. More information on Keyconfig is available in the Mozillazine forums. After installing it, go to Tools -> Keyconfig and look for "Insert Clipping" in the list of command names. Select that to change the shortcut key combination. Here's a screen shot: