There is a way to avoid the login requirement, if you want to enlarge a photo or video, or read its accompanying text. I'm not an Instagram user, and I never will be. But, sometimes I want to read a post by a friend or a business.

While viewing the gallery page for an Instagram user, right click on the post you want to access and select "Copy link location," or whatever your browser calls it, then paste the link into a new tab.