I think its not possible , since you need WebSlingPlayer plugin installed for your browser. There are plugin versions for Firefox and IE for PC , but unless someone ports the plugin to fennec on N900 it won't be possible.

Browsing with my S605th N97 browser results in an error message "Your browser is not supported".

Still no dedicated Player for symbian 5th edition. 3rd Edition works like a charm.

Hopefully we will get support for it, but it doesn't look good in the near future. I am planning to get a hava setup, because it looks like it's not that far away from N8x0 implementation. Quality on a screen like the N900 will be nearly the same.