I am using Mail and Firefox. Suddenly today, when I click on a link in an email, the browser navigation to that URL no longer works. When I click on the link, the browser comes to the foreground, but the URL is not passed into the browser and whatever was previously in the browser remains, rather than navigating to the linked page. I remember having this issue year ago in the Windows world. I am not aware of any changes to Mail or Firefox preferences. As a test, I changed the default browser to Safari, and the links from emails work normally. What controls or blocks this function in Firefox?