Eu finalmente encontrei este post
Existe uma maneira de tem perfis do Firefox e alterna entre eles?
que incluiu esta resposta:
About -no-remote switch
- There's another parameter
-no-remote
which you can use to have more than one profile opened at the same time.- There can be max one Firefox instance opened without this parameter, and infinitely many opened with this parameter
- You can also open Firefox always with
-no-remote
switch. However, this comes with a drawback. Read below.Keep mind that if:
- Firefox is your default browser
- you click a link in an external application (say, Word, PDF reader, or IM),
then:
- it will be opened in the Firefox instance opened without
-no-remote
.- If you opened all instances of Firefox with
-no-remote
, you'll get an error message and the link will not be opened.
Esse foi o meu problema. Eu estava com a impressão (errada) de que todas as minhas sessões tinham que ter a bandeira -no-remote. Obrigado @ jakub-g