well first of all there is a "stable" release as well if you look at the bottom of the page provided. the entire reason I am using these builds is because toc is enabled and I can't read a technical book without.

you need to uninstall on the n900 the app and if I recall the associated library which will be the same version number, then reinstall the library (library name is in the link along with the fbreader app). If I recall the second most recent development version worked (whichever that was a month ago) but not the latest. again I am just using "stable".

after uninstalling the app and ?libzlibrary? (think that is the library name) simply click the links in the browser and it will give you the choice to install via application manager. do the library first.

keymapping are in the menu accessed at the top of the screen. If you take stable you have to hit the little dot on the right to go to that tab if you take a later development build you just scroll down. my mapping is as such (I find it very ergonomic)

comma key=decrease font
back arrow (upper right hand corner)=increase font
return key=previous page
move right key (bottom right)=next page
up key = scroll line up
down key = scrill line down
period key = previous toc item
left key = next toc item
L key = open library
space key = toggle full screen
P key = open toc
K key = cancel (for instance if viewing toc this will return you to current book)
O key = access options or preferences (again use K key to move back to book
Q key = quit
B key = open previous book
I repeated a few keys in the name of ergonomics

R key = prev page
T key = next page
E key = scroll up
D key = scroll down
W key = prev toc item
S key = next toc item

hope this helps...