How to fix “Firefox is already running” error
Sometimes when you try to start Firefox, it warns you that Firefox is already running. The message looks like this:
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.
Usually, you can just kill the firefox process to solve this problem. For example, on Linux the command “ps auxwww | grep firefox” will find the process number and then “kill [processnumber]” will work fine. But sometimes things are more horked than usual. That happened to me today, surprise surprise 
Here’s how to fix the deeper problem:
Step 1. Find your profile. This page tells you how to find the location of your Firefox profile. Under Linux (e.g. Ubuntu), it will be at ~/.mozilla/firefox/[Profile name]/ .
Step 2. Remove the lock files. This page tells you what the lock files are for Firefox on Windows/Linux/Mac. Under Unix/Linux, you’ll need to remove two files “lock” and “.parentlock” .
I haven’t had this happen before today, but it can happen if (for example) someone turns your computer off while Firefox is running.
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Teodor Filimon Said,
January 3, 2007 @ 12:09 am
Strangely enough my computer froze yesterday when i was browsing in Firefox - had to manually reset. Today when i started the browser it knew what happened and asked me if i wanted to restore the session (no error..).
However, i got the error described in this post some time ago when i tried to launch Firefox. You know when you launch something and it sometimes takes (longer than expected) time to actually start (although you can see the process in Task Manager) ? Dunno why that happens, but that time when i launched Firefox it was the same. Didn’t know what happened in the beginning, so i launched it again. That’s when i got the error.
Atanas Yanev Said,
January 3, 2007 @ 2:15 am
Matt, you are lucky you got this for first time
This always happens to me - the resolution is far more simple in windows - ctrl+alt+del - then locate and “end” ‘firefox.exe’ process
Worse situation is when you lost all your bookmarks and buttons - you have to go to your profile, location something like this:
C:\Documents and Settings\%UserName%\Application Data\Mozilla\Firefox\Profiles\dasc0fxi.default\bookmarkbackups\
in bookmarkbackups are - guess what? - backups of your bookmarks
Copy your most recent version in C:\Documents and Settings\%UserName%\Application Data\Mozilla\Firefox\Profiles\dasc0fxi.default\ and rename it to bookmarks.html (first remove the older file)
That’s to restore the bookmarks
For the buttons - simply delete “localstore.rdf”, located in C:\Documents and Settings\%UserName%\Application Data\Mozilla\Firefox\Profiles\dasc0fxi.default\
Hope this was useful
Nunya B Usiness Said,
January 3, 2007 @ 3:19 am
This happens to me when I goof the sharing of firefox bookmarks via a share drive and common profile file. I dual boot an XP and FC5 machine with my users have their mozilla profiles on a share. If I use the wrong filename (misread letter l for the number 1 for instance) I get the error message.
Partially Behind Dave Said,
January 3, 2007 @ 5:55 am
It is quite annoying huh Matt, good stuff…I wonder how many people just restart.
Aaron Pratt Said,
January 3, 2007 @ 6:30 am
Just got a copy of Ubuntu in the mail, for those who want to try it go > https://shipit.ubuntu.com/
Thanks for the tips!
benny t Said,
January 3, 2007 @ 7:00 am
firefox is a great browser, the problem is that it is starting to behave more and more like his un-official brother…..
there are 3 main issues that i got with FF:
1-memory cosnumer…
2-Slow activation-my winxp is restarting daily…
3-images on websites not looking so good.
great blog!.
drew Said,
January 3, 2007 @ 9:14 am
I get that firefox message many days a week. I consider it a major bug: not only should ffox fix its own corruption, but it should not be able to get into (or even near) that state.
Obviously the web browser is going to be the main program we run on our computers. Yet if I said I wanted my IM tool, my word processor, my web page viewer, my shell, and my MUA to be all in one big process with one shared memory space, unable to be run simultaneously on multiple boxes (with shared home dir), people would accuse me of throwing out 20 years of OS development.
The ffox folks probably say they’ve “optimized for the common case” or they’re “making things convenient for their users by locking all the profile settings to one process”. I don’t get it, though. I can share my volatile imap inbox across multiple processes (on multiple boxes), but my barely-changing set of trusted SSL certs is too difficult to share between two long-running web browser processes?
Rob Sullivan Said,
January 3, 2007 @ 10:15 am
I’ve been using Linux for a while but not too familiar with all the linux commands - I prefer the GUI so I go to the System Administration tab in my menu, then system monitor - you can easily find and kill any bad processes here.
I find I do this with Firefox a lot but also media players - VLC seems to be the worst for this - you can run multiple instances but it starts to bog the system down when you get 2 or 3 going at once (that is 2 that didn’t properly close in the first place plus the one you are currently using).
This method works (as far as I know) on Fedora, Debian and Ubuntu as I run all 3 of these at home.
Sean Carolan Said,
January 3, 2007 @ 10:29 am
We actually wrote a custom script for our Linux desktop users that would check for and remove the lock files *every time* they started Firefox. A quick and dirty workaround, no doubt, but having ten end-users complaining about this problem multiple times per week got to be unbearable.
I will say that Firefox 2.0 seems to be a bit better about this problem though.
crazyj Said,
January 3, 2007 @ 5:02 pm
I’ve had the same problem here on some networked iMacs. I ended up writing a script to fix it and then I used Platypus to make it a clickable app.
This is for Mac OS X. Adjust the paths as necessary. (As you can see from the “Phoenix” line I’ve been using it a while.
#!/bin/sh
### Remove the Mozilla Lockfile
find ~/Library/Mozilla/Profiles -name .parentlock -exec rm {} \;
### Remove the FireFox Lockfile
find ~/Library/Phoenix/Profiles -name .parentlock -exec rm {} \;
### Remove the FireFox Lockfile from the NEW location
find ~/Library/Application\ Support/Firefox/Profiles -name .parentlock -exec rm {} \;
Marius Said,
January 6, 2007 @ 4:47 pm
You can receive that message if your operating system allows more than one user connected at the same time (Windows 2003 for example).
If you’re logged in on the PC, using Firefox and you connect from another computer to your computer and log in using the same account, when trying to start Firefox you’ll get that message because the lock files exist but the Firefox in the remote connection can not access the Firefox from the other session.
I’ve actually reported this “bug” a few months ago to the team and i got stupid answers, the conclusion was that they won’t bother to fix this. (didn’t argue further, it was pointless)
They also mentioned a possible workaround, here’s the bug listing and the workaround:
https://bugzilla.mozilla.org/show_bug.cgi?id=348721
Thomas Said,
January 7, 2007 @ 5:54 pm
I do’t personally use Firefox frequently, but am a bit of an experienced *nix admin.
Is there any easy way to tell Firefox to store it’s lock files somewhere else? Specifically, in /tmp or your OS’s equivalent, designed for such things and typically cleared out by the OS when the system is started, thus avoiding the computer-shut-down-with-firefox-open-and-left-the-lock-files-behind issue completely?
Richie, Spain Said,
January 10, 2007 @ 3:28 am
Firefox was great at first however I feel personal that browser wise Firefox is slipping and others have caught up. I’ve gone back to IE and the new browser is great, you’ve pointed out one problem with firefox but I feel there is a lot more wrong.
oral seymour Said,
January 11, 2007 @ 11:46 am
I’ve encountered this problem many times in the past, not since I upgraded to 2.0. I love firefox and the thousands of extensions that are available for it
Peter, Germany Said,
January 16, 2007 @ 1:20 pm
First of all: IE is NO alternative for dual boot systems
Second:
if you follow this instructions, http://www.geektimelinux.com/index.php?q=node/view/362 you might experience the problems described above.
We could fix the problem with plain symbolic link instead of regular path.
Works great.
Juan_in_ FL Said,
February 12, 2007 @ 8:56 am
Thanks for the great post. This happens to me way too much in Firefox. The fix is a lifesaver!
Andrew Said,
June 7, 2007 @ 2:10 pm
I only get that problem because I like to run multiple Firefox profiles (at once or not) and I had to modify the shortcuts to look something like this:
D:\Program Files\Mozilla Firefox\firefox.exe” -p profilename -no-remote
This problem pops up when Firefox is running and an external application tries to open a new Firefox window (for example, from help file, or pdf file or whatever). I still haven’t found a way to solve this
CrHasher Said,
June 16, 2007 @ 4:23 am
ON windows XP:
Just go to C:\Documents and Settings\%Username%\Application Data\Mozilla\ and delete all…
Daniel Said,
July 6, 2007 @ 5:09 pm
Andrew,
YOU WROTE: “This problem pops up when Firefox is running and an external application tries to open a new Firefox window (for example, from help file, or pdf file or whatever). I still haven’t found a way to solve this.”
SOLUTION: Right-click on “My Computer”, then click “Properties” > “Advanced” (tab) > “Environment Variables”. Under “System variables”, delete the “MOZ_NO_REMOTE” variable.
I had the same problem you described, and this solution worked for me. Hopefully it will work for you also!
Mathew Said,
August 31, 2007 @ 6:37 am
One can get the ‘Firefox is already running’ error message in another way too as it happened to me. There was no running firefox process and there were no lock files in the profile directory. The problem was that the profiles.ini file contained a defunct profile name like this:
[Profile1]
Name=Default User
IsRelative=1
Path=sz23zs32.default
Default=1
Because of the Default=1 line, firefox was trying to open the sz23zs32.default directory which didn’t, in fact, exist. Deleting the above lines from the profiles.ini got my firefox back up again.
Wesam Said,
September 20, 2007 @ 8:33 am
Thanks a lot, it worked !!
Zak Said,
October 6, 2007 @ 6:27 pm
Hi Matt
killall will take a process name as opposed to a process id.
killall firefox (when you really mean to, of course :P)
It’s part of the psmisc package if you don’t have it installed by default.
Elizabeth MCGuire Said,
November 7, 2007 @ 2:47 pm
I 8use mozilla fire fox. i keep getting error ads need to be loaded from adcode. what is the problem and how can i fix it. when visiting a website it keeps saying windows cannot find null.
Sim Said,
November 23, 2007 @ 1:49 pm
Unfortunately, none of this hasn’t worked for me. I have no lock files, I have Administrator rights, and I’ve even reinstalled FireFox to no avail. Avast hasn’t found any viruses but something is deadly wrong. After I reinstalled FireFox still had 2 profiles I had created beforehand. Can anyone help? My IE isn’t saving cookies and Safari is not ready for prime time.
Shameer Said,
December 22, 2007 @ 6:00 pm
Been wanting to use firefox for a weeknow and it didnt work. renaming the profile sure did the trick. Thank you.
chano Said,
January 27, 2008 @ 1:34 am
we use firefox on windows XP because it’s much faster than IE, but yesterday we downloaded themes for our firefox and just so happened that our firefox started to display “Connection Reset” and we can no longer use the browser. And even if we uninstalled our existing firefox, and installed a new one(same version and other versions), it still produces the same result. Does it has anything to do with the themes? how can we fix this problem? we definitely want to use firefox again! please help, thanks.
Justin Said,
January 29, 2008 @ 8:39 am
Daniel: I have the same problem Andrew has, but I don’t have a MOZ_NO_REMOTE environment variable set anywhere. Like Andrew, I’m using the -no-remote command-line switch, not an environment variable, in order to run multiple instances.
This problem occurs even if I have only one instance running, so long as that instance is not using my default profile.
My GUESS is that when you click on a link, it wants to activate your default profile. If I only have one copy of firefox running, and it’s using my default profile, then clicking on the link will work. If I have two copies running, then clicking on the link won’t work. If I have only one copy running, but it’s NOT using my default profile, then clicking on the link won’t work. Sometimes it’s annoying and cumbersome to get the URL to copy-and-paste it: e.g., if you get an email with a link in it.
Judy Said,
February 3, 2008 @ 5:21 pm
What if I can’t delete the “parent.lock” file?
Everytime I try, a window comes up saying “Cannot delete parent: The file or directed is corrupted and unreadable.”
=/
Nevyn Said,
February 11, 2008 @ 4:14 am
Hi Judy,
If you’re using windows, you can try this program:
http://www.topdrawerdownloads.com/download/104402
Otherwise, if you’re using Linux, at a command prompt, type in:
lsof ~/.mozilla/firefox/[Profile name]/.parentlock
If nothing shows up there, you’ve got a much bigger problem. You’re going to have to umount the file system or mount it read only mode and run fsck (file system check) on it.
Judy Said,
February 16, 2008 @ 10:36 am
Thanks Nevyn,
I downloaded the Unlocker program, but it still didn’t delete the parent.lock file.
And I have no clue what you mean by umounting the file system?
Ronnie Said,
February 28, 2008 @ 1:06 pm
If mozilla is displaying this because you are on a network with a roaming profile which happens alot you just go to C:\Documents and Settings\%Username%\Application Data\Mozilla\Firefox and modify the profiles configuration settings to another path, or remove completly and save, this should keep this from happening.
Thanks Ron
Mitt Said,
April 7, 2008 @ 3:48 pm
Justin, Daniel, Andrew: This might be a bit late but this is how I got around this same problem. I created two shortcuts to my Firefox (one for the default profile and one for my second). For the default profile I left the shortcut path at its default value (C:\Program Files\Mozilla Firefox\firefox.exe) but for the second profile I added the -P and no-remote switches (C:\Program Files\Mozilla Firefox\firefox.exe -P “Profile Name” -no-remote). While I had this problem I was using the -P “Default” -no-remote on my default shortcut (where I think the problem was)
JoshP Said,
June 7, 2008 @ 8:21 am
I have windows xp media center edition OS.
Firefox says firefox is already running please close it to open a new.. blah blah blah you know the deal.
Already tried going into task manager, not there so i cant end firefox.exe.
I’ve reinstalled, i’ve restarted.
Anything else i should try???
Christian Said,
June 16, 2008 @ 4:40 pm
i am having a error and i have been having for a while it says that fire fox is already started and i must close it the case is that is will not show up on my prosses can some one please help?
Richard Barrington-Hill Said,
July 4, 2008 @ 3:06 am
Hey all - to fix this problem I wrote a batch file (If you have windows folow this:)
Open Notepad.
Paste in the following :
———–Copy Below Here————-
@echo off
setlocal
set exeName=%~1
if “%~1″==”" set exeName=”firefox”
if “%exeName%”==”" echo Processing aborted&pause&goto :EOF
call :GETNAME “%exeName%”
set found=
for /f “tokens=*” %%a in (’tasklist ^| findstr /i “%fileName%”‘) do set found=Y
if “%found%”==”Y” call :endfirefox
taskkill /f /im “cmd.exe”
:GETNAME
@cls
set fileName=%~nx1
goto :EOF
:endfirefox
@echo off
@cls
taskkill /f /im “firefox.exe”
“C:\Program Files\Mozilla Firefox\firefox.exe”
taskkill /f /im “cmd.exe”
exit
———–End above here————-
Save as killfirefox.bat (it’s important it saves as a .bat and not a .txt).
Place it on your desktop - if you get that error message simply run the batch file, and it’ll fix it AND start your browser for you.
Nice