User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-GB; rv:188.8.131.52) Gecko/2009042316 Firefox/3.0.10 Build Identifier: 184.108.40.206 I use Visual Basic code that opens Thunderbird to send text message or email and it has been running perfectly well for years without any problems. After upgrade to 220.127.116.11 it now produces the following error message: "Either there is no default mail client or the current mail client cannot fulfill the messaging request. Please run Microsoft Outlook and set it as the default mail client". NOT IN A ZILLION YEARS! When I uninstalled 18.104.22.168 and reinstalled 22.214.171.124 my VB code and Thunderbird worked together perfectly as they always have so problem is definitely with the upgrade. Reproducible: Always Steps to Reproduce: You need my code I have a PDF file showing the code and various screen prints with error messages on them. Happy to send through. I'm back using 126.96.36.199 and everything's fine again but unless I get to hear this bug fixed will not be able to upgrade again.