9 April Update: I may have been mistaken about the problem extending to Ubuntu, as it appears not to be the case today. I spent a little while looking into the problem on my wife's Mac, and it appears to be related to the encoding settings in the browsers, and the font sets saved into the system. It would make sense that the fonts are affecting it, because my wife downloads a bunch of strange fonts for her design business. But this shouldn't affect the primary fonts selected for use by the browser.. so it's still a mystery and not fixed.
Something is terribly wrong with Twitter on my Ubuntu running Chromium, Mac running Chrome and Safari, and Tweetdeck extension to Chrome on both operating systems. A search reveals no help. Anyone else having this display problem? See photo: