Short addendum – already on April 9, 2019 the developers of Mozilla released version 66.0.3 of the Firefox browser (available for Windows, Linux and macOS). It is a maintenance update that fixes some bugs. I had already seen it on Thursday, but dropped it because of blog and DNS problems. Details about the update can be found in the release notes. The browser can also be downloaded here. Thanks to Andreas and DiWÜ for the comments.