It's not "make it work in each browser", and it's not "just too much". If you spend an additional couple minutes per assignment checking functionality in major

It's not "make it work in each browser", and it's not "just too much". If you spend an additional couple minutes per assignment checking functionality in major browsers (ignoring IE), you're set. For your FeatureA, I'd ignore IE (that's a whole college course in itself), but I'd grade that 9.8/10. -0.2 cause it looks weird in Safari.