Firefox version : 141.0 (64-bit) in openSuse Tumbleweed. This is a fresh install of everything because it's a new machine. I used Firefox sync because we can't do the old thing of importing a pre-existing profile - it doesn't do what it says it should... There are two behaviours in my old setup which no longer work, but which are related. 1. If I open a link in Thunderbird it should, if an instance of Firefox is already running, open in a new tab of the existing Firefox window. It doesn't. It opens a new window. 2. If I click on an external link to a site (ie one that points to another site) it should open in another tab. It doesn't. I have tried the solutions suggested on this site and they don't work.