What OS? What version of Firefox? Here's what AI says. https://www.google.com/search?q=firefox+is+already+running+but+is+not+responding+on+Horizon+VDI+terminal+server&client=firefox-b-1-d&sca_esv=b4f1a4e5dd378925&ei=f-_VZ-70ApGq5NoP_O3SwQE&ved=0ahUKEwiusLGtgo2MAxURFVkFHfy2NBgQ4dUDCBA&uact=5&oq=firefox+is+already+running+but+is+not+responding+on+Horizon+VDI+terminal+server&gs_lp=Egxnd3Mtd2l6LXNlcnAiT2ZpcmVmb3ggaXMgYWxyZWFkeSBydW5uaW5nIGJ1dCBpcyBub3QgcmVzcG9uZGluZyBvbiBIb3Jpem9uIFZESSB0ZXJtaW5hbCBzZXJ2ZXJI0yNQuQdYsBhwAXgBkAEAmAFUoAH7AqoBATW4AQPIAQD4AQH4AQKYAgWgAssCwgIKEAAYsAMY1gQYR8ICDRAAGIAEGLADGEMYigXCAgoQABiABBhDGIoFwgIFEAAYgATCAgYQABgWGB7CAggQABgWGAoYHsICCxAAGIAEGIYDGIoFwgIIEAAYgAQYogTCAggQABiiBBiJBZgDAIgGAZAGCpIHATWgB7Mc&sclient=gws-wiz-serp

Hi jonzn4SUSE, Windows Server 2019 Version 1809 17763.5567 Firefox 133.0

I have restarted all the servers the user is logged in on. it doesn't work.

The only finding I see is AppData>Local>Mozilla>Firefox = There is no user specific "Profiles" file. it doesn't seem to be creating.

Yes, I have looked into these solutions. There is no result yet. https://support.mozilla.org/en-US/kb/firefox-already-running-not-responding

It will be difficult for someone to troubleshoot unless they have access to a similar environment. Sounds like a job for someone in a Horizon VDI terminal Server forum. Maybe someone at Mozilla has access to a similar setup and can chime in.

Hi jonzn4SUSE, The problem is solved. I saw that Horizon VDI Firefox profile files are kept in a different location.

As suggested in the solution, I deleted AppData>Local>Mozilla>Firefox profile files. I recreated them.

Thank you for your suggestions.

OUTSTANDING!!!