Cleaning is a part of optimizing - but it's not the whole cleaning routine.
It'll clean other browsers if you tell it to (I recall that the latest version is set to clean Firefox by default). Just click on the Applications tab to see what it lists. You can also customize it to clean other locations - but I haven't used that function myself.
I don't like PC Booster or PCPitStop - they take a generic approach that just isn't (IMO) appropriate to the concept of optimizing. Optimizing has to be done (again IMO) with the focus on a particular system and how it operates. While there are some common denominators, there are many differences that could result in less than optimal performance if you use those tools.
That being said, it's harder to properly optimize a system than it is to run one of those tools.
I'd suggest that you leave the other tools in CCleaner alone for now (just use the cleaner). They are a great part of the program - but they are so powerful that one wrong decision there can hose your whole system. BTDT (Been There, Done That!

)
In particular, the only registry "fixer" that I recommend is the one at
http://safety.live.com/ It was developed by Microsoft, and they're the one's who developed the registry.
Also, don't "fix" your registry very often. It doesn't need a whole lot of routine maintenance - and if asked, I'd recommend no more than once every 6 months or so. Overcleaning the registry has bad effects over time, even with Microsoft tools - so let it alone unless you know that there's a problem with it!