Instagram started testing a horizontal feed for some users, provoking the predictable expressions of outrage on social media.

The new interface had users scrolling side-to-side to see posts, instead of the traditional vertically scrolling experience. As the test rolled out, users were less than pleased.

A few of the online reactions:

Instagram chief Adam Mosseri issued a social media mea culpa this morning, saying the test went more broadly than planned.

A few minutes after the horizontal feed went live, everything reverted to normal.