question abt element widths

i tried adapting a spacehey grid code to here, but it shows up differently between safari and firefox (the browsers i use). 

i'm not done yet (esp haven't added all my mobile adjustments), but for those on desktop: what's the width of the blurbs? is the space filled, or is there a weird gap? depending on which one seems to be the more common width, i could adjust the blurbs width. generally, should i try to follow safari or firefox's execution of code?

thank you for any input ㅠㅠ