Hello,

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove your Firefox program files and then reinstall Firefox. This process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location.

To do a clean reinstall of 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 mozilla.org (or choose the download for your operating system and language from this page) and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (or open the Firefox menu and click the close button ).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows: (Note: Check both folders.)
     • 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.

WARNING: Do not use a third party uninstaller as part of this process. Doing so could permanently delete your Firefox profile data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be easily recovered unless they have been backed up to an external device! See Back up and restore information in Firefox profiles.

Please report back to say if this helped you!

Thank you.

I don't know how to find a desktop version of Firefox. There is just one download button

The 2 C: drive Mozilla Firefox folders each have 93 items but none of them is installer except a tiny text file. Is there another name?

You can usually find the Firefox installation folder in one of these locations:

• (64-bit Firefox) "C:\Program Files\Mozilla Firefox\"
• (32-bit Firefox) "C:\Program Files (x86)\Mozilla Firefox\"

As I said before, there is nothing labelled "Installation Folder" in those locations. Just a text document listing all the files that were installed.

Perhaps I should delete the entire Program Folder?

The folder you are looking for where Firefox is installed is named "Mozilla Firefox". "Installation Folder" is merely meant to point out that Firefox is installed in a specific folder and you shouldn't look for "Installation Folder", but look for "Mozilla Firefox".

Thanks for the responses. By saving an exe file, I installed a new version of Ffox with a bunch of directions about losing my profile unless I set up an account. I am still working on that but appreciate the responses.

18/09/2019 : I was using Firefox yesterday with no problems. I logged out of the internet then returned to FF at around 22:00 hours (UK) when it came up with this message (I copied it into notepad) :

XML Parsing Error: undefined entity Location: chrome://browser/content/browser.xhtml Line Number 2958, Column 11:

         <button id="protections-popup-trackersView-settings-button" <="" pre="">
^
I cannot access FF at all now. I am using Google Chrome to post this message. Per the Mozilla website a new release that automatically blocks trackers has been released. I do not know about it blocking trackers, but it has most certainly blocked me !!!
As this error has occurred after a Firefox upgrade, why don't you fix this error at source ?
Why is there no word wrap in these replies ?
</button>

18/09/2019 : This is the Firefox window that first appeared yesterday.

Hi LJones

There has been a update released today (69.0.1), so it is quite possible that something went wrong with installing this update (maybe your security software kept a lock on some files).

You can do a clean reinstall like posted above and remove the Firefox installation folder to ensure that all files get replaced. Latest Firefox version:

• https://www.mozilla.org/en-US/firefox/all/

24/09/2019 : I followed the install/uninstall advice above late yesterday and Firefox now works. However, it has lost all of my Bookmarks !!! How do I get this data back and more to the point, where is it ?

Another point, the uninstalled FF was in the Program Files (x86) folder, but the new version is in the Program Files folder (put there by the install wizard). There is a Mozilla Maintenance Service folder left in the x86 Folder and it was updated yesterday, during the install.

EDIT - I have found the file 'Bookmark Backups' and the one Application Basics points to is EMPTY !!! There is another Bookmarks Backup file with my data, under another folder, so how do I get the Application Basics to point to it ?

If you previously had a 32-bit Firefox version and switched to the 64-bit version that installs in a different Firefox program folder then Firefox will create a new profile.

Firefox 67 and later can use a dedicated profile for each of the Firefox update channels and will lock the profile, so it can only be used by Firefox in a specific installation folder. For Release versions this profile would be a xxxxxxxx.default-release profile, profiles used in older Firefox versions usually used a xxxxxxxx.default profile (a refresh adds a time stamp).

• https://support.mozilla.org/en-US/kb/dedicated-profiles-firefox-installation

If you lost personal data then it is possible that a new default-release profile folder has been created. See "Determine if Firefox has created a new profile":

• https://support.mozilla.org/en-US/kb/recover-lost-or-missing-bookmarks

You can open the about:profiles page via the location bar to check whether multiple profiles are present and what profile Firefox currently is using.

• Do NOT click any Remove button on this page.
• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

The screenprints below show the two folders that have my FF Profile.

The first is the folder FF points to, but the Bookmarks folder is empty.

The second folder (1490) has all my data, but FF does not point to it, so I cannot access my data from the previous version.

How do I get FF to point to the correct folder?

You can delete compatibility.ini in the second profile that has your personal data if Firefox refuses to use this profile.

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

cor-el said

You can delete compatibility.ini in the second profile that has your personal data if Firefox refuses to use this profile.

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

Firefox keeps looping ... 01} I switch it to the folder with my profile data and log out. 02} I restart FF but it tells me to create a new profile 03} FF will not open until I have done that, afterwhich 04} It reverts to the new profile... which does not have my data. 05} Goto 01.

So how do I get FF to permanently recover and use my profile data???

To make these posts I am using Google Chrome. If I do not get a satisfactory answer to this problem then I will dump Firefox.

Update.

I removed that compatability file to desktop (rather than delete it, just in case(!) ) . Firefox opened saying it was having trouble restoring my previous session, so I started a new session and ...

It is back to normal, so thank you for your help, Cor-El.

I solved this way.

Navigate to %appdata%\Mozilla\Firefox\Profiles\[your profile]

Rename the folder "extensions" to "_extensions"

Run Firefox, then quit it.

A new empty "extensions" folder is created.

Delete the new "extensions" folder.

Rename "_extensions" back to "extensions".

Run Firefox.

That's it. It worked for me.

25/10/2019 : Once again I cannot access Firefox as this Parsing Error has returned TODAY. Rather than have all us users faff around with re-installs, why don't the Firefox programmers TEST their updates BEFORE they issue them and eliminate this problem at source ???

I am using Google Chrome to post this, NO thanks to this latest Firefox Parsing Error screw up.

This can happen if you have language packs installed that weren't updated properly. You can check the Languages section on the about:addons page and check for updates.

30/10/2019 : I have re-installed FF today. It is working normally and has recovered all my bookmarks.

This time I first uninstalled the Mozilla Maintenance and the Mozilla Firefox program itself via Control Panel, Programs, Uninstall, followed by the Firefox Setup program on my desktop.

I then (via Google Chrome) came to this Site and downloaded FF. It detected that FF had been installed before and offered a Re-Install, which I accepted.

I am posting this reply in Firefox.

LJones said

25/10/2019 : Once again I cannot access Firefox as this Parsing Error has returned TODAY. Rather than have all us users faff around with re-installs, why don't the Firefox programmers TEST their updates BEFORE they issue them and eliminate this problem at source ??? I am using Google Chrome to post this, NO thanks to this latest Firefox Parsing Error screw up.

Did you try my solution? Didn't work for you?