Are you talking about the Zoom Controls from the Customize Palette, or zoom buttons provided by an extension like NoSquint?

neither will work

The Zoom Controls from the Palette are working for me in Aurora 5.0a2, with no extensions installed.

Try disabling NoSquint and see if the Zoom Controls from the Palette work. There may be an incompatibility with 5.0 and NoSquint, which might disable the buttons from the Palette.

As recommended, I disabled NoSquint and now my palette zoom controls are working.