It's bugged me for a while that Firefox (on Windows 7) seems really "zoomed in" compared to other browsers, even after using ctrl-0 or the zoom menu to make sure its zoom level is 100%.
Chrome left, Firefox right. Both are set to 100% zoom, but they're clearly interpreting it differently. Everything's massive on Firefox, and a lot of things (even the UI buttons) are fuzzy. What's going on?
Just to confirm that they really are both 100% zoom, in Firefox:
...and in Chrome:
Curiously, IE by default is zoomed to the same level as what Firefox calls 100%, but it calls it 125%.
When forced back to 100%, IE matches Chrome's 100%: