Firefox has always shown status messages at the bottom of the window during the initial page loading and also when you hover a link (overlink message). It is possible to hide these messages via code in userChrome.css.

Are you referring to these messages or if your issue different ?

Unfortunately that's not it. It definitely is an ad based what ever. I managed to grab a printscreen of it which I've attached.

I haven't been able to tell which extension/feature produces it.

I would run in safe mode for sometime to see if you still get that ad popup. If you don't see it then it could be an add-on you're running.

Thank you BUT all my systems are/have been Linux based. I could not find a compatible version of what you recommended.

I noticed that and changed my post.  ;-)) The only popup like that I've seen come from notifications or Web Push. It could be this. see screenshot https://support.mozilla.org/en-US/kb/push-notifications-firefox?as=u&utm_source=inproduct

Could be your connection. You are using Firefox from the Mozilla server ?

You can check the connection settings.

• Settings -> General -> Network: Connection -> Settings

If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.

See "Firefox connection settings":

• https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

You can see all registered service workers on these pages:

• about:serviceworkers
• about:debugging#workers

You can check WebSockets via this page:

• about:networking#websockets

See also serviceworker.txt in the profile folder.