Instagram has significantly updated its mobile website such that it’s no longer necessary to install the network’s app to post photos or view the Explore tab. This may improve access to the social network in areas with slower wireless networks.

Until now, you could only browse the platform from the mobile site. Posting anything to Instagram required the mobile app. (accessed from mobile) is a web experience optimized for mobile phones. It’s designed to help people have a fuller experience on Instagram no matter what device or network they are on.
– Instagram

Instagram still isn’t letting people post content from a desktop computer, so it’s continuing to emphasize mobile usage.

The mobile site doesn’t let you upload videos or send direct messages, at least for now.