This problem might be caused by an add-on injecting links to that server in Google search results, or otherwise activating on Google pages. In a Reddit thread, one called CrossPilot was mentioned, but there may be others.

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. On the right side, find the "Manage Your Extensions" heading.

If there is at least one extension before the next heading -- "Recommended Extensions" -- please continue:

Then cast a critical eye over the list below that heading. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious or that you just do not remember installing or why? Anything you can live without for 24 hours? If in doubt, disable (or remove). For your privacy and security, don't let mystery programs linger here.

Any improvement?

Thanks. I tried to replicate the problem on Google Chrome without issue. Changed search engine from Google to Duck Duck Go, removed worldwide radio as this was the last add-on (strangely the problem started after it did some sort of update) and the issue appears to have gone.