I'm running Thunderbird 52.1.0 on Windows 7 and have Firefox set as my default browser. When I click on a link in an email I've received, Thunderbird returns a screen "link Properties" which shows the URL for the link. There is no way I've found to bring up the web page other than copying the URL over to Firefox. Up until a week ago, I was able to click the link and the web page opened in Firefox (which is what is suppose to happen). I've tried turning off my security system and also dropping back to Thunderbird 45.8.0 Neither has fixed the problem. Is there some Thunderbird file which probably has become corrupted or some config. setting which has gotten changed? If no one knows the cause, I guess I'll have to backup my contacts and email, delete all the Thunderbird files and do a clean install which I'd rather not do but I do want to fix the problem.

I have the same result, the "link properties" window opens if I try to open a file attached to the email. The file will not open.