As the Blogger.com continue to evolve, the engineering team today announced that the new features, Dynamic Views, previewed in March, and Web Fonts both require advanced browsers that support HTML5. Older browsers just aren't able to provide you with the same high-quality experience.
For this reason, "Beginning August 1st, we'll support the current and prior major release of Chrome, Firefox, Internet Explorer and Safari on a rolling basis. Each time a new version is released, we'll begin supporting the update and stop supporting the third-oldest version," stated Brett Wiltshire, Product Operations.
Wiltshire said that "As of August 1st, we will discontinue support for the following browsers and their predecessors: Firefox 3.5, Internet Explorer 7, and Safari 3."
It's because, in these older browsers you may have trouble using certain features in Blogger as well as many other Google Apps such as Gmail, Google Calendar, Google Talk, Google Docs and Google Sites.
[Source: Blogger Buzz]