Well I don't blame the Mozilla folks, the browser needs to be "re-invented" since it has started to be come more than "just" an application to view websites. the EA Origin application pushes the limits by spawning a browser window which in turn spawns a game (read: Battlefield 3). Basically this excatly what Steam does but instead of writing their own browser engine they are using the one you already have installed.
HTML5 has also blurred the lines on what a desktop application is over a web one by borrowing media support from the host system. So, if you have a high quality audio player the browser will use that to play music instead of relying on what Flash implementation has been provided. As a web developer I am a little torn on how HTML5 works but do welcome the change.
“Maybe we shouldn’t even call it a browser anymore,” Mozilla’s VP of Firefox engineering Jonathan Nightingale told me a few days ago. “‘Browser’ is really an antiquated word. People don’t really browse all that much anymore.” Instead, he argues, we now mostly use our browsers to access sophisticated web apps, web-based productivity tools and social networks.
For browser developers, this means they have to start to rethink what their browsers should look like now that usage patterns have changed and that the majority of users have become pretty experienced Internet (and browser) users.
I'm not a fan of the new user interface, making Firefox look like Chrome is just proving that Chrome won the "new" browser wars. I hope this isn't the start of a downward sprial for the browser but, I have faith and will support them whenever I can.