A friend of mine passed along a potential fix for the annoying Firefox copy and paste issue. So far it has worked pretty well for me:

(1) Close Firefox
(2) Create a file in C:\Documents and Settings\UserName\Application Data\Mozilla\Firefox\Profiles\default.ext named “user.js” [Note: this may be ext.default]
(3) Add the following to the file:
user_pref(“capability.policy.policynames”, “allowclipboard”);
user_pref(“capability.policy.allowclipboard.Clipboard.cutcopy”, “allAccess”);
user_pref(“capability.policy.allowclipboard.Clipboard.paste”, “allAccess”);
(4) Start Firefox