Client is very bugged.

[Trainboy15]

Singleplayer textures are missing + crashes unless in single-thread mode, server list shows "No Connection", even though the MOTD is very much there. Can't connect to any server
Using UT13: http://test.tuffis.online/files/1_1UT13/WASM/

[UplandJacob]

Firstly, singleplayer is not a priority and is, and has been, completely broken.

Secondly, due to weirdness with the WispCraft injector, server connections with the Web Runtime of UT13 are completely broken. Use the Offline Download instead (you can host it if needed), and you shouldn't have this issue (WispCraft won't work, but SyntaxSavy is working on a fix; at least regular servers will work.)