Just got curious about the new version (beta) of Fennec and first tried to follow the instructions on http://firefox.com/m/beta . However – that one didn’t realy work since the repository which was added is not for the beta but for the release – meaning I got 1.1.
After some digging on the mozilla server I found the right repository which is:
URL: http://moff.mozilla.com/latest-beta/maemo/multi/
Distribution: fremantle
Components: release
Adding that one and disabling the other mozilla repository got me Fennec 4.0b2 installed.
Have fun playing