Nearly all the main players in the browser world have their own blogs and while they might range in their usefulness they can give you an interesting perspective on the vendors ideas of themselves.
The obvious missing link above is from Apple, is the WebKit blog better for Apple than having their own? The fan-boys run Safari anyway. The WebKit blog focuses mainly on the visual elements they add and improve (CSS transitions etc), with the more tech elements (Eg. JavaScript performance) listed but given second billing.
At Mozilla, Firefox is just a category, it’s not got it’s own blog. Recently it’s very focused on security and updates.
Chrome’s blog is really new, although there is an older blog for Chromium concentrated on performance and stability
Opera’s blog re-forces their position, unfortunately. The underdog’s blog is all about getting the word out from their tight following, the tech elements play second fiddle. The Opera developer area is great though …