Stopping Second Instance of Firefox Trying to Start

I am running 13.2 64 bit and Firefox 43.0-53.1.

I have a problem when I have Firefox running and I click on a new link for example provided in an email. Instead of opening the link in a new tab in Firefox, the system tries to start a new second instance of Firefox.

This gives me the bouncing Firefox logo for a while and then the link then opens in a new tab on the first instance as required but the second instance sometimes opens too and other times stops and closes.

The result is long delays and chaos.

How may I stop this please? Is it a Firefox problem or some other helper setting somewhere?
Budgie2

That’s possibly a problem in the email software, and the way it handles links.

If you start firefox with “no-remote” (or whatever it is called), then your email software cannot communicate with that instance of firefox, so attempting to start a new instance is likely.

Hi and thanks for the suggestion. Seems probable but I cannot yet find anything resembling “no-remote.” Will keep looking.
Thanks again,
Budgie2