Running multiple Firefox at the same time
I have two firefox: Firefox(normal version) and Firefox Developer Edition. Today morning, I deleted the Firefox Developer Edition by AppCleaner and re-installed it, then something weird happened.
When I opened the new Firefox Developer Edition then launched my unchanged Firefox, the Firefox cannot be opened and it showed an error: A copy of Firefox is already open. Only one copy of Firefox an be opened at a time.
AFAIK, the multiple Firefox instances are able to run at the same time,
if they use different profiles.
Therefore, I opened about:profiles on Firefox to check it.
From above, the setting was incorrect. It should use Profile: default instead of Profile: dev-edition-default. That’s why I cannot open Firefox and FirefoxDeveloperEdition at the same time.
To fix the problem, I simply click Set a default profile under Profile: default, then closed it, and relaunched it to check the setting.
I also checked the FirefoxDeveloperEdition’s setting
to make sure everything is fine.
I wrote this to remember how I fix it, in case the same problem happens again.