Right now our localStorage implementation for child processes makes a synchronous call to parent processes whenever data is accessed. This part is necessary and not a big deal. However once we get into the child process, the current implementation is done by accessing the normal localStorage implementation. The problem with this is that the localStorage implementation of course does synchronous IO. This part is not necessary since we can wait with answering the child process as long as we want. I.e. we can do asynchronous IO in the parent process and only once that is done return and unblock the child process. It's also much worse since doing sync IO in the parent process has dramatic effect on performance in the parent process. I'm making this depend on bug 600307 since we're doing a complete rewrite of localStorage there. It technically probably is possible to fix even in the current implementation, but it doesn't seem worth spending time on until we have the new, cleaner, implementation.