Last Firefox should certainly work. I've seen that the 3 pixel window when the service that is sending the filetree can not open the files/directories on the share, or when the share folder is empty. Those cases need their own warning dialog windows on the GUI, i will ad them for future versions.
Could you just restart the job manager changing the Shared folder to any where a mxs is (even if it is not shared with the render, just to test the filetree on the browser) I would prefer that being the case, as otherwise it could be that somehow the filetree daemon is stuck on your setup and it will be very difficult to reproduce the cause ...
Thank you for your time TurboGlider,