Mozilla/Firefox is really kicking things into gear and this week's relaunch of the app site with integrated community options should continue to keep them on the major growth path...
Article suggests Google is just starting to rev up the engine but I imagine they are going to go after Firefox with a lot of resources. I'd bet chrome will see some significant growth in 2010.
I thought the bundling of add-ons that work well together was a really neat idea: a social productivity bundle might include Amplify, yammer, Zemanta, etc...