Unable to open Firefox and Firefox Developer Edition at the same time


Getting this error: A copy of Firefox is already open. Only one copy of Firefox can be open at a time.

Just installed the latest version of Developer Edition. Running 58.0.2 (64-bit) on regular Firefox. macOS High Sierra 10.13.3

Did a restart too, no luck. Any ideas? Thank you

(Baptiste Thémine) #2

You need to create a new profile in order to run two Firefox side by side. See instructions on https://support.mozilla.org/questions/1149213.

(J. Ryan Stinnett) #3

By default, Developer Edition is meant to use a separate profile so that it can be run side by side out of the box. @Tyler-Atl, were you using it side by side successfully before, and then it changed after updating?


Thanks for the replies. It looks like when I migrated to my new Macbook, my old Firefox profiles were corrupted, so regular Firefox was using the ‘default-developer-edition’ profile.

As suggested, I used the profile manager to sort it out. I renamed the working profile to ‘default’ and then launched the Developer Edition (which must have created a new dev edition profile):
/Applications/Firefox.app/Contents/MacOS/firefox-bin -profilemanager

Thanks again!

(Dave Bonner) #5

Adding a comment here in case anyone else runs into my variant of this issue.

I had FF beta channel installed side-by-side with the developer edition on a Mac, and last week it seemed like the beta channel install had flushed my profile data. But I went to open developer edition just now, ran into the issue mentioned above, and discovered that the beta channel had just switched to opening the developer edition profile by default somehow.

(James W. Alvies) #6

This is the non-language specific URL: https://support.mozilla.org/questions/1149213 in case you don’t speak French.