@sgunhouse Yes i have a high definition monitor. I have been using the Zoom extension with 5% increments for while but I find these days that it doesn't always retain settings for some reason so I want to ditch it and use the native facility.
Thank you. The information there indicated it is Bitdefender interfering with the site with its own certificate. Switching off Bitdefender encrypted web scans fixed the problem. Unfortunately adding my site to exceptions and restarting the encrypted web scans should have fixed the problem but didn't. Bitdefender support are trying to ascertain why.