In Firefox, after I log in to Roudcube, when I click on the Inbox, I get the error: Server Error! (Forbidden). It is fine in Chrome and MS IE. The error console shows:
Timestamp: 09/09/2013 11:03:51
Error: TypeError: me.messagedialog.dialog is not a function
Source File: http://webmail.mydomain.com/skins/larry/ui.js?s=1376301457
Line: 293
PHP Version 5.4.19
Plesk 10.5.30
Roundcube Webmail 0.8.6
Firefox 23.0.1
Chrome Version 30.0.1599.28
MS IE 10.0.9200
Try upgrading to RoundCube 0.9.4.