Ok what version of Firefox are you trying to install and on what Windows OS version?

Last time I saw this message it turned out the OP was trying to install a recent Firefox version on Windows XP.

If you have Windows XP or Vista then you can only use (32-bit) Firefox 52.9.0 ESR at the latest and note it is now EOL. http://archive.mozilla.org/pub/firefox/releases/52.9.0esr/win32/

If you have 32-bit or 64-bit Windows 7, 8 (8.10, or 10 then you can run current versions Firefox 62.0 Release or 60.2.0 ESR www.mozilla.org/firefox/all/

Also just to be sure, make sure you are not trying to run any version of Firefox in Windows XP or Vista Compatibility mode on Windows 7,8,10.

So I tried to delete the new update switch had changed it to 60.2 I do I put it back to the 54.9

Hi you should if you can update to the version posted 52.9.0esr as it is the most secure and stable browser and the last.

Might want to think about moving to Linux

I know how do I uninstall the 62.0 that is on there now

Hi, with hard trouble since you put 54 in also.

Always :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Make sure that the bookmarks are the same in both versions and your not missing any. if are copy both Profiles out :

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Since you have 2 and done the above : https://www.revouninstaller.com/revo_uninstaller_free_download.html

Do what it wants, point it in the right directions.

Reboot, uninstall it. and Reboot.

Then Get a DOS Command Prompt up typing cmd.exe in search Right Click Run As Administrator then Copy/Paste/Type : SFC /Scannow SFC<space>/Scannow to fix registry errors.

Install 59.2.0