This is why the environment I use for developing automation (a dedicated VM) is different than my actual desktop where I do all my other work. That way I don't "pollute" my clean room with clutter of documentation, open browser instances, etc. I'd highly recommend doing something like this.
In the meantime, most modern browsers (IE, FireFox, Chrome) have the ability that, when you close a session, you can have it "save" all your open tabs so that, when you re-run the browser, it will pick up where you left off. So, when you start your "playback" to check what you've done, close and save your browser tabs first, then run your test.
Think of it as the same thing you would do in a manufacturing environment... you don't test a substance, device, machine, etc., in an environment with a lot of variation... you strictly control the environment so that tests are repeatable and assured to be unaffected by outside influences. Perhaps not always in a "clean room" but any QA lab at a manufacturing firm would have controlled environments for their tests. In our case, you're testing a web page in a particular browser. Anything else running on that machine, including other browsers, could potentially pollute your "sample" making your test unreliable.
