A feature I loved a so much on OS X is the Safari smart zoom (like double tap an area in Safari on an iphone/ipad). I do not like reading blog articles or any kind of texts with a small font size. Instead I prefer to read in full screen (27' iMac).
Iceweasel is a Debian version of Firefox which mainly change the name and the logo (with some Debian patches) which means that the Firefox add-on work.
There is one which do exactly what I want and it's Zoomr. Install it and then hold the click on the area where to zoom. : )