OK, now it works. I had "new tab override" installed pointing to Google. All worked fine until I updated to Firefox 77.0.1. Then I got the "X frame" error. I loaded Ignore X-frame-option plugin but could not make it work. Then uninstalled both new tab override and ignore X-frame-option. When receiving the developer response I realoaded both and now it works. Not being a Firefox guru, I have NO idea why but now I am very happy bunny. Many thanks.