Add NoScript to Firefox and you have a deal, but enable the top-level domain option, which makes it much more friendly. Best free anti-virus at the moment is
Avira. Rather than Adobe Acrobat, get
Foxit Reader.
If you have data you want to safeguard, I recommend
Dropbox, which instantly backs up any data you put in its directory, and lets you roll back changes.
Skype is great, too.