tried the solutions here? https://support.mozilla.org/en-US/kb/Hyperlinks-in-Messages-Not-Working

It may well be your anti virus program blocking URL links from the strange new program it does not know is safe (A new Thunderbird version), check security suite firewall, browsing and phishing controls.

Thanks for the reply.

I tried everything I could find, including the instructions in that link, but nothing worked.

My A/V is Vipre - good suggestion but I have no idea how one would allow in Vipre.

Anyway, I was today at the point of doing a reformat of my C drive (I do this every year or so and thought that might help!) but for some unknown reason the links have started working again! Slowly, after clicking it takes about ten seconds to open Firefox/ a new FF tab, which used to be instantaneous.

Standard diagnostic for anti virus is windows safe mode with Networking. That way you don't have to change anything in the anti virus until you have to. So I will borrow heavily here by quoting the standard response as it contains links to how to get into safe mode with networking for all the popular operating systems..

To diagnose problems with Thunderbird, try one of the following:

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

To change the application associated with http, https, or ftp links, I had to do the following:

- Open thunderbird Tools | Options | Config Editor

Type in search bar: network.protocol-handler.warn-external Then change the settings on these three entries from FALSE to TRUE, by double-clicking each one. network.protocol-handler.warn-external.ftp network.protocol-handler.warn-external.http network.protocol-handler.warn-external.https

Close config editor

- close the config editor window

- click on a link in an email. This should now open a window.

You may possibly need to exit Thunderbird and re-open it first. - WoodBTech -

Worked for me !