I don't use Foxit, Sumatra or Adobe Reader cos I don't need to edit PDF files.
Please forgive me, I'm not trying to be disrespectful. Rather than worry about plug-ins that could slow down your browser or cause other issues, why not install one of the many free PDF readers like Foxit, Sumatra, Nitro, etc? Just because you don't edit PDF files doesn't mean you can't use one of these products as your default reader. (I'll bet most people don't use half the stuff available in Windows 7 but they still buy it and install it.
If you're worried about taking up hard drive space, you might consider Cool PDF Reader. It has a very
small footprint. Cool PDF Reader - View PDF, Free PDF Viewer