>Address space shortage will likely be covered by the tab unloading feature mentioned in the article, before it becomes an issue in practice.

before? I've seen Firefox run up against the 2gb limit[1] for years.

This 4GB space is evenly divided into two parts, with 2GB dedicated for kernel usage, and 2GB left for application usage. Each application gets its own 2GB, but all applications have to share the same 2GB kernel space.

[1]: http://www.brianmadden.com/blogs/brianmadden/archive/2004/02...