If you want to use Firefox behind a proxy and need to tell it to bypass a range of addresses, this is how you do it:
Press Alt-O, Network, Settings
In 'no proxy for', use the following values.
10.0.0.0/8 will allow 10.*.*.*
10.0.0.0/16 will allow 10.0.*.*
10.0.0.0/24 will allow 10.0.0.*
For example, 188.8.131.52/16 will cover the range 184.108.40.206 - 220.127.116.11
(i.e. keep the left 16 bits = 2 octets = '1.2')
For more examples of how this works, visit this CIDR calculator
ps: Comments and/or links to this article are most welcome!