Add these lines to C:\Program Files\eXe\Mozilla Firefox\greprefs\all.js

Search for these lines:

user_pref("capability.policy.default.Clipboard.cutcopy", "noAccess");
user_pref("capability.policy.default.Clipboard.paste", "noAccess");

and change them to this:

user_pref("capability.policy.default.Clipboard.cutcopy", "allAccess");
user_pref("capability.policy.default.Clipboard.paste", "allAccess");

Our firefox distro already contains this change.

You can also use Shift+Ins instead of Ctrl+V