You can eliminate large swaths of the internet from loading in your browser and control what sets of sites are blocked when.
I change up the image every few days but I try to have it point to something like the recent Orion launch or a trip photo from the Portland Hikers Field Guide. Instead of redirecting to Google's homepage (which is what I did at first), seeing the image gives me positive reinforcement to pause and be more mindful about what I'm doing, where my head is at, etc.
It's been an enormous help in instilling my habit to stay focused.
Just having that schedule imposed on me for a few days was all it took for me to get out of the habit of opening a new tab and heading to one of the aforementioned sites any time I ran into a difficult problem. I've noticed an increase in my productivity, and I don't really even feel the need to twiddle away that time anymore.