Grid lines would need to open an issue at GitHub - openstreetmap/openstreetmap-website: The Rails application that powers OpenStreetMap but I actually think those grid lines are ok and informative (so I would recommend to open an issue if you think otherwise and want the website team to ask why those appear and if that is intentional).
Blurry: yes, it’s just overloaded servers for tile.osm.org (besides the problem that those 256*256px tiles will always be a bit blurry depending on the screen dpi).