Please post a screenshot of the Save for web settings and we'll try reproducing at our end.
What is your Windows Version?
What are your display settings for text and apps? > The screenshot below is from a Win 10 PC.
And this is what I found out on my tablet, may be it's the same in your case:
In Chrome, Firefox and Opera your picture is blurry at 100% because it is in effect enlarged at 150%. So I have to set the zoom to 67% for a crisp look. (150% * 67/100 = 100%).
Internet Explorer 11 and Edge know this special feature and adjust the 150% view "in the backend" to 100% view and your picture is sharp.
Some programs scale, some don't.
Though I'm using Windows 7, your guess was right: I had my Windows Display Settings for text and apps set to 101%. Setting it back to 100% seems to have solved my browser issue and everything looks great!
Thank you so much!! Marking as solved.