I am using version 22.0. Firefox updated itself a week or so ago and ever since then, when Firefox opens up (with my saved tabs) or when I click to open new tabs, all websites open in 200% zoom. I have to hit Control - twice to get to the "normal" zoom view every single time.
Also, my left-hand side Bookmarks menu looks different too - they look like they are also zoomed in but I can't figure out how to zoom out of that area so that I can see all my bookmarks like I used to.
None of my other programs are having any kind of zoom issue so I know it's related only to Firefox. I have rebooted many times over the past week or two and that doesn't solve the issue.
I've also tried going to View / Zoom / Reset - but that takes me BACK to the 200% view.