The profile page and subpages (activity, profile, and changing settings) when displayed on my Macbook in both Firefox and Chrome (e.g. mine) is a little too wide. It seems to be caused by the link in the top right to the Network profile on the profile tab and the small user icon and name in next to the link in the activity and settings tabs:
This is a small problem, but looking into this could be useful for keeping other pages working well and implementing the eventual responsive design — I am pretty sure it is caused by the width of the window being miscalculated, because if the dock is set to hide and the window is resized to fill the whole screen, this problem does not occur and the page fits perfectly. This problem happens on profile pages on all SE sites I tested, including SO and Teams.