Long time to open address book
From MozillaZine Knowledge Base
If it takes a long time to open a local address book it may be due to a bug found in versions 1.5 to 126.96.36.199 that adds bogus lines in your pref.js profile file every time you open your address book or use the contact sidebar. When enough of these bogus lines collect, they can create a significant delay the first time that you do anything that involves the addressbook in your in your Thunderbird session. This can slow down opening the address book itself or the contacts sidebar, and delay the autocomplete function when composing mail.
This bug was fixed in version 188.8.131.52 and all 2.0 releases, so these bogus lines should no longer be added to your users.js file once you've installed a version beyond 184.108.40.206, however any bogus lines already present will remain until you remove them.
This bug report describes how blocks of preferences beginning with ldap_X.servers._nonascii_ or ldap_X.servers.user_directory_ (where X is a number) might be added. The ._nonascii_ or .user_directory_string (depending on exactly which version created it) is supposed to be used when the address book entry has non-ASCII characters.
How to fix it: