http://wiki.x2go.org/x2goplugin doesn't say anything regarding compatibility so I guess the statement on the x2go wiki should be updated by someone with edit rights so newcomer's don't get frustrated trying something that's not supported.
On supported systems, this plugin acts as a web portal which can be used to access an x2go session via any java enabled Web browser (Firefox, IE, Opera) instead of using one of the x2goclients