$ firefox -UILocale en-US # starts mozilla-firefox $ firefox -UILocale en-US # starts second mozilla-firefox (you will be prompted which profile to use) while $ firefox # starts mozilla-firefox $ firefox # opens new window in running mozilla-firefox tested with versions: mozilla-launcher-1.42 mozilla-launcher-1.45 Reproducible: Always Steps to Reproduce: 1. 2. 3.
I can't seem to reproduce that here... Have you tried upgrading to mozilla-launcher-1.49 or later? This is the version I'm using, and I'm successfully able to start multiple windows while specifying UILocale.
This bug is awaiting user response... Cannot reproduce either.