Browser will not start up

If Firefox or Mozilla Suite fails to start then this article may help. (If it starts up but won't load any web pages, then read this article. If it starts but your bookmarks or other settings are gone, read this article.)

Profile locked

If you attempt to start Firefox or Mozilla Suite and receive a "profile in use" error, or in Firefox 1.5 and later, "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." that means the profile is locked. Ending the running process and restarting the browser will normally unlock the profile. If not, see this article for further instructions.

Firefox will not start after installing or updating McAfee SiteAdvisor

Firefox may fail to open after installing or updating the McAfee SiteAdvisor Firefox extension [1] or after an update to McAfee software that includes the SiteAdvisor component [2]. According to this SiteAdvisor support article, the problem occurs because of a conflict between SiteAdvisor and automatic proxy configuration scripts in Firefox. Either end the firefox process that remains in memory, start Firefox in Safe Mode and uninstall the SiteAdvisor extension from the Tools -> Extensions window or follow the workaround given in the SiteAdvisor support article. If SiteAdvisor is installed as part of a McAfee software package such as McAfee Internet Security Suite, you can selectively remove just the SiteAdvisor component using the McAfee uninstaller, e.g., via Windows Add/Remove programs. [3].

Windows-specific problems

"The program must close to allow a previous installation attempt to complete. Please restart."

If you are receiving this message when attempting to start Firefox and a restart has no effect (bug 283680):
Open the Firefox installation directory (usually C:\Program Files\Mozilla Firefox) and delete the file "xpicleanup.dat" [4].

Windows Vista: Open the C:\Users\<your_username>\AppData\Local\VirtualStore\Program Files\Mozilla Firefox folder and delete the file "xpicleanup.dat" (you may need to first end the "xpicleanup" process, if found, in Windows Task Manager and delete the file "xpicleanup.exe" in the Firefox installation directory) [5].

"Error opening file for writing..." on Vista

Firefox may require you to be logged in as an administrator. As a workaround, to launch Firefox, right-click the icon and choose "Run As Administrator".[6][7]

"JS_DHashTableOperate could not be located in the dynamic link library js3250.dll"

If you attempt to start Firefox 2 and receive the error, "The procedure entry point JS_DHashTableOperate could not be located in the dynamic link library js3250.dll", it indicates a faulty installation caused by upgrading from an earlier Firefox version without exiting all firefox.exe processes (bug 357890). Uninstall Firefox (or delete the file "firefox.exe" from the installation directory), make sure that firefox.exe is not active and then reinstall Firefox 2.

Mozilla Suite fails to start

If Mozilla Suite fails to start after restoring a previous registry or other system change, delete the "GRE" folder located here: "C:\Program Files\Common Files\mozilla.org\GRE" and then reinstall Mozilla Suite (Bug 211694).

Mac-specific problems

If Firefox does not display a browser window, quit Firefox using Cmd+Q, open ~/Library/Application Support/Firefox/Profiles/<garble>.default/, and remove "localstore.rdf". Restart Firefox. Any toolbar customizations or window placement changes you have made will be lost [8] (Firefox 1.0.x).

Linux-specific problems

Ownership

If you used "sudo" to install Firefox and it starts at the end of the install process and runs when you log in as root but fails to run as a normal user, then check the ownership of "$HOME/.mozilla" and subdirectories. The symptoms are that you won't get any error messages, and Firefox will exit with a value of 1. The ownership of "$HOME/.mozilla" and subdirectories may be set to "root:root", and you will need to execute

chown -R <username>:<usergroup> $HOME/.mozilla

at the command line to get Firefox to work (Firefox 1.0.x).

Similarly other users on the system may need their ".mozilla" folder 's permissions changed using "chown" as shown above.

Fedora 4 libstdc++

When you run from the console window the command /{path to download location}/firefox/firefox you may see

/usr/local/firefox/firefox-bin: error while loading shared libraries: 
libstdc++.so.5: cannot open shared object file: No such file or directories

On Fedora 4, you need to install libstdc++ by running yum install /usr/lib/libstdc++.so.5. After running this, rpm -qf /usr/lib/libstdc++.so.5 should print compat-libstdc++-33-3.2.3-47.fc4.

"/lib/i686/libc.so.6: version 'GLIBC_2.3' not found required by /{path to download location}/firefox/libxpcom.core.so"

If you see

/lib/i686/libc.so.6: version 'GLIBC_2.3' not found required by /{path to download location}/firefox/libxpcom.core.so

or something similar when starting Firefox, then the library is not new enough to support Firefox 1.5 and possibly previous versions. Updating GLIBC is not advised as other applications depend upon it. If possible, migrate to a newer Linux distribution with an updated version of GLIBC.

Other solutions

Perform the standard diagnostic.