Do you really need to be that thorough in your testing? What are the costs when a bug gets into production and needs fixing? What are the costs of testing and fixing it before it goes into production? Balance it.
We're only doing developer ad hoc testing. We just click through a few things when we develop a feature (something you're doing anyway, I assume) and then put in production. We don't do exhaustive testing. If an edge case doesn't work and it gets reported, we'll fix it then. This has the added advantage of only working on problems customers really consider problems.
This works because a web application can be pushed online very quickly, so you can make many iterations and fixing a bug isn't inherently harder when it's in production or in development.
This is a huge YMMV-topic, where you should really think of both sides of the equation. Something that doesn't happen too often in Internet-articles, I'm afraid.
