Just tried fbreader, renaming it to fbreader180 and using extensions.cfg.
I got 'cannot start program'.
So I guess it's different for the PB 602.
I do hope the PB 602 will get more attention. Documention has some big gaps. I configured the wifi but there's no way to use it. No apps like a browser or such (only games), etc.
The model is not even mentioned officially in the forum.