Gmail has two primary display modes, depending on what type of browser1 you use to access it. Standard view is what you’ll see when you sign in to Gmail from a fully supported browser, and gives you access to all Gmail features.
If you don’t have a fully supported browser, we still want you to have access to Gmail; that’s why we’ve developed a basic HTML view of our service that’s compatible with almost any browser. If you sign in to Gmail using a browser that isn’t fully supported, you’ll automatically be directed to the basic HTML view.
The basic HTML view is a little different from what you’re used to because the following features aren’t available:
If you’re directed to the basic HTML view of Gmail, but would like to try using the standard Gmail view, you can try to visit http://mail.google.com/mail?nocheckbrowser. Keep in mind that standard view may not work, even with this link, if your browser isn’t supported. [source]