Do i have to delete/clear anything in Firefox after creating offline keys using Bitaddress? If i use Bitaddress in Firefox offline to create key pairs, will any info remain in Firefox/anywhere else that i will have to delete  - i mean, if i then use that Firefox to connect to the internet after making the keypairs, could somebody potentially obtain any of the keypair info?
The whole idea of bitaddress is that your addresses are dynamically generated. As such, the only place it would be is in the browser cache or RAM. Rebooting the computer will clear the RAM and deleting the browser history (preferences->privacy->clear your recent history) should clear the cache.