When in doubt, try CCleaner from Piriform.
CCleaner is a free download and also should be installed as freeware (check carefully when downloading). There's also a payware option but I've never used it.
CCleaner works on your registry files and browser cashe (not sure about Firefox), so pay attention when you run it. A little time spent during the scan and cleaning set-up pays off.
The actual cleaning cycle runs fast.
Based on my style of browsing, I only need to run it a couple of times per year as a check, but it does what it says and works great.