http://kb.mozillazine.org/Profile_in_use

http://kb.mozillazine.org/Opening_a_new_instance_of_your_Mozilla_application_with_another_profile

The first, you can do a word search for: parent.lock

The second, if you get into wanting two profiles open at once, describes how.

NEXT: If you use the launch flags, … -P -no-remote, as I do having seen that recommended online, but you use those flags w/o knowing what’s going on, those links together help explain it.

I hope this is helpful more than additionally confusing things for readers. It has helped me understand the launch flags I use. (For WinXP users – Either the flags can be used to launch Firefox from the control panel, or if a desktop launch shortcut is or has been created for Firefox it can be edited by right-click on the shortcut icon, select properties, and editing on the “target” line adding the launch flags.) If that’s at all confusing be careful, if it makes sense, try it. You can google:

firefox launch switches “-p -no-remote”

for Mozilla links about that switch setting. Next, as an easy habit-to-form alternative to the batch file use SafeBrowser suggests, before exiting a firefox session, open your profile folder, and after you are certain the exit has finished, refresh the folder and if you have a zero-byte parent.lock file after the refresh, you can easily delete/rename it. If the file is not zero-bytes or you cannot delete/rename a parent.lock file after the complete exit, it probably means you have a somehow corrupted profile so Firefox locked it; and you need to take the troubleshooting link steps SafeBrowser gives. In case it helps – Two easy ways to open the CORRECT profile file are from AppButton > Help > Troubleshooting Information; or if you have Nightly Tester Tools installed [even if not using Nightly it is a useful addon] opening the profile is a submenu choice. If you want to disable compatability checking, rather than using Nightly Tester Tools for regularly doing that, checkCompatability 1.3 is an addon for that purpose, and you can disable it and relaunch if you want checking re-enabled.

Last, if wanting info on the built-in (and still in use) profile manager, not the JGriffin standalone, this link:

http://kb.mozillazine.org/Profile_Manager

But if you have multiple Firefox windows open, AppButton ->Exit is required [or if you keep the menu bar open, Files ->Exit]. That’s probably the best practice in any event, using the program’s built in EXIT function.

That is my recommendation – track an exit’s completion before trying to relaunch, or use a specific “restart” addon which is coded to do so. Again, the only time I got the “profile in use” message is when impatient and not allowing a complete exit. And the built-in Firefox profile manager in the Windows version, when invoked, may be called onscreen before the exit is completed, if you exit and relaunch that way. I have not had any problem exiting one profile and launching with another, just as two profiles can be in use on a system simultaneously. I expect the same need-to-wait for a complete exit holds true with the standalone utility JGriffin authored.

That was really a helpful comment from SafeBrowser. I bookmarked it.

This said, the time to give us a corrected version of “ProfileManager v1.0″ is long overdue : 4 releases of FF .
” If you proceed to load Firefox on the SECOND warning, you could damage your Profile.” It is not acceptable by a normal user to have to ignore the first warning and not the second. Normally he does not know that !

Mozilla wanted a way to detect recurring Firefox start-up crashes that occur within a specified time range (6 hours, I believe) on a user’s system. When the number of Firefox start-up crashes occur within the time constraint exceeds the limit in the first pref below, the user is forced into Firefox Safe Mode to try to resolve the issue causing the crashes by disabling extensions/themes-personas/plugins or using the Reset function in Firefox to create a new profile and, 1 by 1 or 2 by 2, etc., reinstalling extensions/themes-personas or reenabling plugins — troubleshooting information and links here (READ THIS ARTICLE AND ALL LINKS CAREFULLY) – http://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems . They decided wrongly, IMO, to use parent.lock as a part of that detection system along with 3 new prefs that you can view in about:config (see – http://kb.mozillazine.org/About:config ). The 3 new prefs are toolkit.startup.max_resumed_crashes and toolkit.startup.recent_crashes and toolkit.startup.last_success. The (1) first pref sets the number of crashes allowed within the aforementioned time constraint and the (2) second pref is present only if there are recent start-up crashes with its value as the number of recent start-up crashes – ONCE ZEROED OUT BY A SUCCESSFUL START-UP, THE PREF WILL DISAPPEAR FROM about:config ON THE NEXT SUCCESSFUL START UP and the (3) third pref is the date and time of the last successful start-up of Firefox in UNIX timestamp (represents the number of seconds since 01/01/1970) and the value for that THIRD pref can be converted to an actual date/time by pasting/typing the pref VALUE in the “UNIX TimeStamp” space and clicking Submit on this page – http://www.onlineconversion.com/unix_time.htm . The way it is supposed to work is detailed in this portion of the Bugzilla report (Comment 18) where this work was done/discussed over very long period of time – https://bugzilla.mozilla.org/show_bug.cgi?id=294260#c18 – DO NOT POST IN BUGZILLA with a complaint; it is for developer discussion ONLY. DO NOT ASK ME ABOUT THE DECISION OR WHY IT WAS MADE BY THE DEVELOPER — I D O N O T K N O W !

DO NOT ASK ME WHY ProfileManager v1.0 has not been changed, when it might be changed, if ever, whether the Profile Manager within Firefox will go away or when. THOSE QUESTIONS ARE FOR OTHERS TO ANSWER — NOT ME!

THE parent.lock FILE IS NO LONGER AUTOMATICALLY DELETED when closing Firefox as it was in Firefox 12 and prior. The parent.lock file is now permanent in Firefox 13 and later.

When using ProfileManager v1.0, you will always get the “profile in use” warning as the code for ProfileManager v1.0 needs to be changed, to agree with the code in Firefox 13 and later, to read and interpret the 3 new prefs. You can safely ignore the FIRST warning, as that is coming from ProfileManager v1.0 as it only sees parent.lock and assumes, with its not-up-to-date code, that Firefox is in use or did not close completely on the previous exit.

**VERY IMPORTANT** – If you accept the first warning (i.e., proceed to open Firefox) and see a SECOND warning, that SECOND warning is coming from Firefox and you need to stop loading Firefox and check to see if Firefox.exe or plugincontainer.exe is showing in Windows Task Manager on the Processes (not Applications) tab. If you proceed to load Firefox on the SECOND warning, you could damage your Profile.

You can post on the Firefox forum with your questions about how Firefox (but not ProfileManager v1.0) is performing its start-up crash function, as well as information about Profiles and other Firefox issues.

You can, as I have done, create a Windows batch file to delete only the profile.lock file AFTER you close/exit from Firefox.

**TIP** – always use Firefox > Exit or File > Exit/Close when exiting Firefox to avoid problems.

Sample batch file suggestion to delete the parent.lock file.
-THIS WORKS FOR ME,
-USE AT YOUR OWN RISK
-BE SURE EVERYTHING IS EXACTLY AS BELOW with the correct path to your Profile
-CREATE FILE USING A PURE TEXT EDITOR, LIKE NOTEPAD
-BE SURE THE FILE NAME EXTENSION IS .bat NOT .txt OR SOMETHING OTHER
-I NAMED MY FILE del_parentlock.bat
-INCLUDE THE QUOTATION MARKS IF THE PATH CONTAINS SPACES – MOST DO
-YOU CAN REPEAT THE LINE BELOW for each path to a different profile if you have multiple profiles.

del “C:\..full path to your profile…\parent.lock”

https://jagriffin.wordpress.com/2011/01/11/profilemanager-1-0_beta1/#comment-356

The retained built-in profile launcher exists in the PaleMoon and IceDragon forks of Firefox too, as in current Nightly, Aurora and beta FF, and uses the same launch flag switches.

Am I correct in the understanding, that if FF ever drops the internal profile manager as was contemplated but not done, I can use the J.Griffin stand-alone utility, but in each profile I need to rename or delete the empty file: parent.lock?

I am confused.

BAM your profile is now unlocked.

I haven’t had any problems with managing my profiles with the Profile Manager app since.

enjoy!

However, if there is I did notice another problem, possibly related to the change in behaviour by FF with respect to the parent.lock file. If I launch my default FF profile using the profile manager, and ignore the warning about the profile being in use then FF starts up as expected but if I try to launch a web page from another application e.g. Thunderbird, Word then I get the following error in a FF pop-up (instead of opening a new tab in the running FF),

>>>
Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system.
>>>

Strangely I also get this error if I launch my default FF normally (not using profile manager) but launch Thunderbird using the profile manager.

But if I launch FF and Thunderbird normally I don’t get the error when I follow a web link in a email message.

I did find Mozbackup since which does work real good.