Log out of your sync account to avoid interference. Visit about:support in the address bar and click the "Clear startup cache" button on the right side then restart the browser.

Are you able to edit browser.newtabpage.pinned in about:config?

Tried them. Thank you but these suggestions did not solve the issue.

Are you using Sync as pinned tabs are part of prefs getting synced?

You can possibly set services.sync.prefs.sync.browser.newtabpage.pinned to false to disable syncing pinned tabs.

You can backup browser.newtabpage.pinned to be able to restore the pinned tabs. You need to close and restart Firefox after modifying browser.newtabpage.pinned in about:config.

I have tried several things and none of it seems to fix it. Thank you

Does it still happen in a new profile? An easy way to test a new profile is to install Developer Edition and see if it happens there or refresh your existing profile. Make sure you stay signed out of your sync account when testing.

None of these strategies solve the issues.

Do you see any active enterprise policies listed in about:policies?

Try disabling any third-party antivirus or security software, this may require rebooting into Windows Safe Mode (networking enabled).