This is a modified version of Profile Switch 1.3.1 that automatically makes your last/current viewed Window be the "Default Profile", making it so when external links are clicked, they will actually open in the window you'd expect them to, like in Chrome.
This version can't be installed on regular versions of Firefox, only Firefox Developer version.
In Developer version, go to about:config
and disable xpinstall.signatures.required
, then you can install this addon modification.
Hopefully the original developer will accept the PR so this won't be needed anymore.