I know how to increase or decrease the zoom level of a page. However, Firefox does not show me anywhere what the current zoom level is. Why? Both IE and Chrome show you the current zoom level. I don't want to install any extensions.
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: