mine said

firefox updated - even after i said no - then on restart i get the well documented . " can't open FF bc one copy is already open" . which of course is not the case else I would not be searching how to solve

Hello mine,

just to make sure; is this the message you're getting :

" Firefox is already running, but is not responding. "

If so, it looks you've already read this article :

https://support.mozilla.org/en-US/kb/firefox-already-running-not-responding

May I ask if you're using Kaspersky by any chance ?

And if so : would you disable it to see if that will solve the problem ?

the actually message is in quotes - "A copy of FF is already open. Only one copy of FF can be open at a time"

i removed old version - downloaded new and still get this msg.

macbook os 10.12.2

Thank you for clearing that up.

Would you please look at this thread and see if anything there (especially the Chosen Solution) will work for you ?

https://support.mozilla.org/en-US/questions/1254772

Also see this thread on Reddit :

https://www.reddit.com/r/firefox/comments/anl1p0/cant_open_firefox_because_a_copy_is_already_open/

I'm sorry that you find it not so easy to post a question here, but the people who answer questions here on the support forum are (for the main part) volunteers, users just like you, who are trying to help other users in our spare time. Nothing we can do to make it easier to post a question - we're not Firefox employees or developers ....

/Applications/Firefox.app/Contents/MacOS/firefox-bin -P

cut and paste in terminal dialogue - y viola - deleted default user profile create new profile open FF and yes -0 . it works - thank you for support ..

mine said

thank you for support

My pleasure - and : well done !