PHP session_start() hangs
When loading a page with a session_start(), the browser just hangs for a looong time.
This usually only affects firefox or chrome based browsers. Internet explorer seems to be immune to this effect.
It seems to be a problem with multiple session_start() calls that are not finished. It seems that previously e.g. Firefox issued an impliciet session_write_close() when a page had finished loading. This is no longer the case, and as that's the case, the session will block indefinitely, or at least a very long time.
Whenever you issue a session_start() command, remember to also issue a session_write_close() command when you have finished writing to the session variable. The content of the session variable will still be available, but will no longer be updateable, unless you open the session variable again.