I can't say I disagree. One way of making these more "complicated" projects more accessible for students is to create tiers of success, say, a bronze, silver,and gold level of "complete"  If that were done here, I might put cross-browser testing in the silver or gold category.

Bronze - bare minimum, could use more exposure and practice
Silver - reasonable expectations, would expect Gold or greater if project were assigned a 2nd time
Gold - exceeding expectations, displaying some comfort (if not mastery) of the core topic