To use, for example, uBlock Origin in Chromium 55.0.2883.75-4, a user has to either launch chromium from the command line: chromium --enable-remote-extensions
or, as root change edit /usr/bin/chromium and change want_remote_extensions=0 into want_remote_extensions=1 or build a Debian package for uBlock Origin. I find neither of these user-friendly ...
