Configuring Mozilla Firefox

Start Mozilla Firefox, ensure only one instance is running
Goto ->options->privacy->cookies
Check 'enable cookies' and 'for the originating website only'
The exceptions and show cookies buttons allow for advanced cookiemanagement. Here you can see and delete cookies and block certain domains (advertisers) from sending cookies. To read about the security risk of cookies go here
Goto ->web features
Check all items, even the 'let sites install software' you'll always be asked for permission when a site wants to install software so this is a safe setting
Goto -> advanced (behind javascript)
Only check 'change images' when you experience problems you can experiment with these settings
Goto ->advanced (tab)->security
Check both items under 'software update'. All items under 'security'
At certificates check 'ask every time' for high security and at validation check 'use OCSP to validate only certificates that specify an OCSP service URL option