Firefox is the most secure browser available, especially if you toss on noscript plugin.
Download and install Malwarebytes Antimalware, which will remove all the Trojans/Viruses/etc that you have gotten from using Internet Explorer.
Download and install Piriform CCleaner, it's a nice tool which will help fix your registry, remove garbage to free up space, and even wipe the free space on your hard drive with the standard NSA 7 pass algorithm, if you want to make it impossible to recover data.
4) No matter what browser you use, Update your Flash. Flash vulnerabilities cause a lot of problems for people.
The above fix the majority of problems the typical user experiences.
Edited, Jul 4th 2010 11:55pm by Vlorsutes