Ronnie Jones shared a screen shot on Twitter of the Google search results, specifically the AdWords listings, showing Google underlining the display URL of the ad.
Ronnie promised there was no extension or third-party behavior triggering the URL to be underlined. He said it is on and off on some browsers in his office, depending on the query and time they search. So I guess it isn't specific to one browser, but maybe a test Google is trying on the AdWords results.
Here is his screen shot:
It looks really bad and ugly to me, so I am still surprised Google would consider testing this but who knows. They've tested uglier UIs before.
Forum discussion at Twitter.