Believe it or not, the fact is Gmail sucks on Opera, now Google is recommending that Gmail users install Firefox or Chrome if they want to see Gmail run "an average of twice as fast." When you log into Gmail using Internet Explorer, you'll see a "Get faster Gmail" link in the set of links across the top of the page. If you follow the link in IE7, you'll find yourself at this page, which claims that Gmail runs an average of twice as fast on Firefox 3 or Chrome than it does IE, Gmail Help.

Source:→ Lifehacker