In Firefox 3.6.4 the default connection settings have been changed to "Use the system proxy settings". See "Connection settings": Firefox can't load websites but other browsers can

You can find the connection setting here: Tools > Options > Advanced : Network : Connection If you do not need to use a proxy to connect to internet then select No Proxy

I have the same problem on Windows 7. Since upgrading to Firefox 3.6.6 [Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.6) Gecko/20100625 Firefox/3.6.6] I am unable to connect to any web sites, although Firefox will open local html files.

Setting "No proxy" does not solve the problem.

Other browsers (IE8 and Opera) are OK.

The problem is that Windows Vista and Windows 7 treat all IP addresses as IPv6 so your PAC file will fail unless you make changes to it or Disable IPv6 completely or BOTH.

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WINDOWS 7 IPv6 disable (though I wouldn't, because it might screw up other M$ things)

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From this web site: http://windows7themes.net/disable-ipv6-windows-7.html

1. Open up the registry.
2. Uncollapse [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\]
3. Next, we create a new 32-bit registry key: “DisabledComponents”: By the way, even if you are on 64-bit system you have to create a 32-bit registry key only, because it only reflects the size of the registry key. A 32-bit registry key can store a maximum value of 2,147,483,647.
4. Enter: “DisabledComponents” when prompted for a name.
5. Double-click the newly created registry key and copy and paste the value: ffffffff (8 F’s) [His documentation only has 6 f’s]
6. Restart your PC and you are done: You just disabled IPv6 in Windows 7!

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PAC FILE CHANGES HERE

REMEMBER to change

var proxyONEip = "192.168.1.100";

var proxyTWOip = "192.168.1.200";

to YOUR FIREWALL IP addresses

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//------------------------------------------------------------------------------------------

// alert ("Notice, This is a pop-up message\n***Use me to debug***");

function FindProxyForURL(url, host)

{

// Convert strings to lower case to avoid character matching issues

host = host.toLowerCase();

url = url.toLowerCase();

// Set proxy IP ADDRESSS VALUES here

var proxyONEip = "192.168.1.100";

var proxyTWOip = "192.168.1.200";

var proxy_no = "DIRECT";

// is client IP odd or even (if IP is ODD then

                    //  proxyONEip/proxyTWOip else proxyTWOip/proxyONEip)

var myip = myIpAddress();

//DEBUG alert("My Addr: '" + myIpAddress() + "' \n");

//DEBUG alert("My URL : '" + url + "' \n");

// split the IPv4 address into a 4 element array

var ipbits = myip.split(".");

// make sure this is an IPv4 address, which is > 1

if (ipbits.length > 1)

{

// we have an IPv4 address here

//DEBUG alert("xIPv4 in play!\n");

//DEBUG alert("My ipbits.length = '" + ipbits.length + "' \n");

// grab the 4th octet and convert it to a decimal

var myseg = parseInt(ipbits[3]);

} else {

// we have a potential IPv6 address here

//DEBUG alert("IPv6 in play!\n");

//DEBUG alert("My ipbits.length = '" + ipbits.length + "' \n");

// split the IPv6 address into a 6 element array

var ipbits = myip.split(":");

if (ipbits.length > 1)

{

// looks like we have an IPv6 address here

//DEBUG alert("Looks like an IPv6 address!\n");

//DEBUG alert("My ipbits.length =:' " + ipbits.length + "' \n");

// grab the 6th octet and convert it from hex to decimal

var myseg = parseInt(ipbits[5],16);

} else {

// NOT AN IPv6 either, so ODD it will be by us forcing it to a 1!!!

//DEBUG alert("Looks like garbage, forcing to a 1!\n");

var myseg = 1;

}

}

// take the modulus 2 of the myseg where 1 = odd, 0 = even

var mycalcseg = myseg % 2;

if (mycalcseg == 1) {

// ODD number (mycalcseg = 1)

//DEBUG alert("My myseg odd is '" + myseg + "' - '" + mycalcseg + "'\n");

var proxyone = proxyONEip;

var proxytwo = proxyTWOip;

} else {

// EVEN number (mycalcseg = 0)

//DEBUG alert("My myseg even is '" + myseg + "' - '" + mycalcseg + "'\n");

var proxyone = proxyTWOip;

var proxytwo = proxyONEip;

}

// Bypass proxy for internal web servers

if (isPlainHostName(host)) { return proxy_no; }

var destinationIP = dnsResolve(host);

if (isInNet(destinationIP, "10.0.0.0", "255.0.0.0") ||

isInNet(destinationIP , "172.16.0.0", "255.240.0.0") ||

isInNet(destinationIP , "192.168.0.0", "255.255.0.0") ||

isInNet(destinationIP , "127.0.0.0", "255.255.255.0") ||

isInNet(destinationIP , "169.254.0.0", "255.255.0.0"))

return proxy_no;

//DEBUG alert("My PROXY = '"+proxyone+":80'; PROXY '"+proxytwo+":80' \n");

return "PROXY "+proxyone+":80; PROXY "+proxytwo+":80";

}

I disabled buggy Internet Explorer 7 by giving it a 0 0 0 0 address. But when I upgraded from FF 2.x to 3.6.15 I found I couldn't connect to internet because 3.6, by default overrides the settings in 2.x to USE SYSTEM PROXY SETTNGS Any attempt to change settings to NO PROXY were defeated by FF automatically redirecting back to proxy settings . Only way to get online was to re-enable IE7!! But I solved the problem by DOWNGRADING to FF 3.5.17 whose default settings are NO PROXY. IE 7 is still disabled and I can get online again. 1 Download 3.5. 2 Uninstall 3.6. 3 Install 3.5. It's simple.

RX to FF personnel-set the default setting to NO PROXY.

SAY WHAT, gotta go back to college and get me a phd.

More on this topic http://topwindows7themes.com/category/windows-7-vista-xp-tutorials