Hello, what do you mean as in "undefined entity"?

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Hello,

First unhide the hidden files and folders:

• http://kb.mozillazine.org/Show_hidden_files_and_folders

Then go to your profile:

• Profiles

Then up to the Firefox folder and now you will see your profile folder rename it or delete it,then try start Firefox again

I followed your steps above. Found profile and deleted it. Got this error when trying to start Firefox: Firefox profile cannot be loaded. It may be missing or inaccessible So i tried uninstalling and reinstalling. Still get same error.

Create a new profile.

• Profile Manager - Create, remove or switch Firefox profiles

Get this error when trying to pull up profile manager..... XML Parsing Error: undefined entity Location: chrome://mozapps/content/profile/profileSelection.xul Line Number 18, Column 1:<dialog <="" p=""></dialog>

That means you need to clean reinstall.

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove Firefox program files and then reinstall Firefox. Please follow these steps:

Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from http://www.mozilla.org and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

Please report back to see if this helped you!

Thank you.

I've followed those steps and clicked on Firefox icon. Nothing happens.

Does it mention which xul (xml) file is causung this error?

Maybe Firefox already running:

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

Also try reinstall Firefox:

• https://support.mozilla.org/en-US/kb/install-firefox-windows

Does not mention any xul (xml) file at all? It doesn't do anything when I click on icon. I'm going to try and restart my computer. This is frustrating.

I did a restart on my computer. Click on Firefox icon and nothing is happening. What should I try now?

Have you tried for a check of malware to see if Firefox is blocked.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

I have Norton360 and it frequently scans and I have no virus. Again, i can install Firefox version 26 and it works fine. They problem is when it updates to version 27.

There are only three entities in line 18 in the profileSelection.xul file. Maybe &windowtitle.label; is causing this issue

<dialog
  id="profileWindow"
  xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" 
  class="non-resizable"
  title="&windowtitle.label;"
  orient="vertical" 
  buttons="accept,cancel"
  style="width: 30em;"
  onload="startup();"
  ondialogaccept="return acceptDialog()"
  ondialogcancel="return exitDialog()"
  buttonlabelaccept="&start.label;"
  buttonlabelcancel="&exit.label;">

• view-source:chrome://mozapps/content/profile/profileSelection.xul
• view-source:chrome://mozapps/locale/profile/profileSelection.dtd
• view-source:chrome://branding/locale/brand.dtd

Guess using Firefox as my browser is a lost cause now. Having been an IT guy for many years, I know you never roll out new updates without being able to fix the issues. A one line link where a person could click on it and the link should execute all the checks to fix any and all issues. I've spent hours trying everything everyone tells me and nothing works. Firefox should resort back to version 26 until they fix the rollout of 27. So long Firefox!!!

Firefox 27 probably works fine for hundreds of millions of users. I wonder if it could relate to something on your setup, possibly some interaction with the Norton software. I would expect it likely Norton software may require up dating for any Firefox version change.

I've had firefox for years and anytime it did automatic update, Norton never interfered before so I'm certain this isn't the case this time either. Time for Firefox to step up!

I wonder how many people Firefox have lost due to this last upgrade? They may have many using it but my guess is they've lost a lot. Even a simple uninstall, delete old folders, reboot, and then clean reinstall should work but it doesn't.

Did you delete the Firefox program folder to do a clean reinstall?

Try to install Firefox in a different program folder by doing a custom install.

I finally stumbled upon the fix. All I had to do was right click on the Firefox icon, go to properties, click on Compatibility tab, and make sure the box was checked for "Run this program in compatibility mode for: Windows XP (Service Pack 2)". It's working for now and I hope continues to work. Any idea why this fix it?