@gychang :-
This 'double tab' thing is nowt to do with Mochi's scripting, Greg. It's nothing specifically to do with Vivaldi OR your set-up, either; it appears to be a long-standing, endemic 'bug' in the Chromium code-base, and for some crazy reason it affects 32-bit compiles to a greater degree than it does 64-bit ones.
I noticed it quite a while back. I use 32-bit Iron as the default browser in some of my 32-bitzers. If I go to open a Thunderbird link in the 'default' browser, up pops Iron, as it should.....but with two identical tabs showing for the same link.
I haven't yet found a way to stop it from performing its party trick, and I gave up worrying about it some time ago. Sure, it's annoying.....but ya CAN live with it. Especially when it's out of your control.
Mike.