Most likely yeah. In 2015 i used Window Maker as my main WM and at least Firefox worked fine with fullscreen videos and from a quick look via git blame support for the _NET_WM_STATE_FULLSCREEN state for _NET_WM_STATE was added in 2009.
However AFAIK that was in the CRM fork which became the main/official version somewhere in 2013 so it is possible your distro at the time had some version from 2006 (which AFAIK was when the last version from the previous developers was made).
However AFAIK that was in the CRM fork which became the main/official version somewhere in 2013 so it is possible your distro at the time had some version from 2006 (which AFAIK was when the last version from the previous developers was made).