Pop up keeps appearing in Firefox

I have a splash page set to “Never show again.” In Chrome and Edge browsers, the splash page is never shown again, even if it is a new browsing session. However it is not the case in Firefox. It is not shown in a new tab, as long it is in the same browsing session. If the browser is closed and reopened in a new session, the splash screen again appears. Is this a browser issue that can be overcome or prevented? I don’t want the splash screen to reappear after it is shown, regardless of browser. Thanks.

Celito