Is it my imagination or has the font of the save dialogue recently become ridiculously and unreadably small?
Topic on VisualEditor/Feedback
Did you upgrade to MacOS X Yosemite ? They have started to use a different default font for such textareas. It's not smaller, but it is less legible at smaller sizes than the previous font in my opinion, due to the kerning.
No, I do not even use a Mac. I am on Windows 7. The problem seems to be specific to Monobook. See this screenshot.
That also applies to other dialogs: therefore, I filed it.