Solving internet connection only for some programs
From The Linux Mint Wiki
I have found repeatedly that after a fresh install Firefox connects to the internet, while programs such as apt/adept/synaptics do not connect, or the other way round or some combination. Sometimes the solution helps if you don't have any connection at all.
I have a router and that causes the problems.
Originally I found out this while trying to get the live CD work (better), so the solution is in the troubleshooter for the live cd.
Troubleshooting_your_Live_CD#No_internet_connection_for_envy.3F
