Firefox is open, click link in Thunderbird & it takes minutes to open in Firefox. Close Firefox, click link in Thunderbird & the link open fast in Thunderbird.
Firefox and Thunderbird are open. Click on a link in a Thunderbird email & it takes minutes (upwards of 5) to open in Firefox. Close Firefox, leave Thunderbird open. Click on a link in a Thunderbird email and Firefox starts and the link opens without hesitation.