Are you using a shortcut to open Firefox? Right-click on it and check its Properties.

Type about:config<enter> in the address bar. If a warning screen comes up, press the I Accept the Risk button. At the top of the screen is a search bar. Type browser.startup.homepage

What is the value? Right-click and select Reset to restore its default value; about:home

Windows shortcut target: "C:\Program Files\Mozilla Firefox\firefox.exe" -p Work -no-remote

about:config browser.startup.homepage Value=https://start.duckduckgo.com browser.startup.homepage_override.buildID Value 20180323154952 browser.startup.homepage_override.msstone Value=59.0.2

Reset all 3. Closed and reopened browser. Problem persists.

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

Problem persists in Safe Mode.

Unlikely to be malware: (1) Malwarebytes does not detect any ad/malware. (2) Problem does not occur on other Firefox profiles on the same computer and same Windows login.

As SalesForce is Mozilla's email vendor, it is more likely to be something on Mozilla's end: "Mozilla receives your email address and a hash of your password when you create a Firefox Account. You can choose to include a display name or profile image. Your email address is sent to our email vendor, SalesForce Marketing Cloud, which has its own privacy policy." Source: https://www.mozilla.org/en-US/privacy/firefox/

I called for more help.

Thanks. Hope someone has a solution. Interestingly, this does not happen when I use the same Firefox Sync account on other computers. So, somehow it is isolated to one Firefox profile using one particular Firefox Sync account on one particular computer and recurs even if the Firefox profile is deleted and a new one is created.

Do a clean reinstall of the current Firefox release and delete the Firefox program folder before installing a fresh copy of the current Firefox release.

• download the Firefox installer and save the file to the desktop
  *https://www.mozilla.org/en-US/firefox/all/

If possible uninstall your current Firefox version to cleanup the Windows Registry and settings in security software.

• do NOT remove "personal data" when you uninstall the current Firefox version, because this will remove all profile folders and you lose personal data like bookmarks and passwords including data in profiles created by other Firefox versions

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

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

• it is important to delete the Firefox program folder to remove all the files and make sure there are no problems with files that were leftover after uninstalling
• http://kb.mozillazine.org/Uninstalling_Firefox

Your personal data like bookmarks is stored in the Firefox profile folder, so you won't lose personal data when you uninstall and reinstall or update Firefox, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.

If you keep having problems then you can create a new profile to test if your current profile is causing the problem.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

Thanks for the suggestion.

I was able to solve the problem by:

1. Uninstalling Firefox
2. Deleting the Mozilla folders in: C:\Users\[User]\AppData\Roaming\; C:\Users...\Local\; and C:\Users...\LocalLow\
3. Reinstalling Firefox
4. Recreating the Profiles and signing into Mozilla Sync

Thanks to both FrankMcD and cor-el for their help.

Glad to help. Safe Surfing.