Firefox opening new window instead of tab.

Despite having the "Open links from other applications in: anew tab in the most recent window" in Firefox 1.0, when I click on a link in an email in Thunderbird it always opens it in a new window!!! Anyone else seen this and fixed it? (SuSE 9.2) -- Tim http://www.bbc.co.uk/ This e-mail (and any attachments) is confidential and may contain personal views which are not the views of the BBC unless specifically stated. If you have received it in error, please delete it from your system. Do not use, copy or disclose the information in any way nor act in reliance on it and notify the sender immediately. Please note that the BBC monitors e-mails sent or received. Further communication will signify your consent to this.