A few scattered suggestions: Create a fresh default profile (no migration) and see if the problem still occurs.
Does the click lockup occur with both the modern and classic skin? Only on the address list or also with other interface components? Review the settings of all ldap, menu, and mouse-related prefs in your profile tree. If you're using any sort of desktop overlay (e.g. XWorkplace), disable it to see if that makes any difference. If possible, try a release older or newer than the one you're using. Also, if you can access a ~equivalent version of Mozilla on another platform, see if the hang occurs there. h~
