In IE, I can say to not use a proxy when the ip adress is: 10.*
If I do the same in Firefox it doesn't work. It uses the proxy when I access a 10.** site.
How can I make Firefox don't use the proxy with a mask like IE?
10.1/999 is not a sensible IP range. I am answering this because at some point this will stop working if firefox validates the IP ranges better in the future. It is possible that 10.1/999 is not matching all of the 10 subnet anyway.
To exclude all of the 10.0.0.0-10.255.255.255 range, use
The 8 means "match any address where the first 8 bits are the same". As an IP address is comprised of 4 x 8 bit octets, 8 means the first octet.
So the following
means "match the first two octets" and so would match 10.0.0.0-10.0.255.255. I
So it follows that 10.1/999 is meaningless. It is saying match the first 999 bits of 10.1.0.0. Given that an IP address is only 32 bits long, it is likely that this is working through a bug rather than intended behaviour.