If you want to see zoom level like IE, you can try this extension

• https://addons.mozilla.org/en-us/firefox/addon/default-fullzoom-level/

If you don't want to install any extensions, then I think at best you might take a look at toolkit.zoomManager.zoomValues preference (in about:config). It gives you information about available zoom levels, but you have to remember how many times zoom in/zoom out actions were used (i.e. there is no current zoom level indicator like in e.g. Opera). For example .3,.5,.67,.8,.9,1,1.1,1.2,1.33,1.5,1.7,2,2.4,3 means that you have:

Levels down (five): 30% 50% 67% 80% 90%

Levels up (eight): 110% 120% 133% 150% 170% 200% 240% 300%