This is a trend that all browsers are following (Firefox 3.0+, IE 7+, Opera). It has been going on for a while. Your best bet is to make your text large enough for everyone to read. Or add some JS to dynamically resize text.
Choose your poison.
Choose your poison.
I guess I hadn't noticed it in FF because the increase for photos with each cmd-+ seems much smaller than in Safari. ...which brings up one more form of inconsistency among browsers. ::giant sucking sound::