This is totally a minor issue, but I was kind of wondering if other have noticed this behavior. Firefox 65.0 fails to display start.ubuntu-mate.org site. I noticed this because although I run a number of different OS's I use the start.ubuntu-mate.org site as my default homepage on all OS's. But the "night" mode doesn't work any more and you can't click into a search window to use either Google or DuckDuckGo. You can see the same page displays fine in Chromium. Any thoughts? I thought it might be an extension so uninstalled all Firefox extensions except Telegram tab.
It's working fine over here...
Might be theme issue maybe? Try changing back to the default UM theme and see what happens.
I don't think it is the theme of the OS, because it appears like this when I use Firefox in Windows 10, Bodhi Linux, and openSUSE Enlightenment DE. All of those OS have different themes that they are using.