xulrunner often freeze at dnsResolve() when using autoproxy

Binary package hint: firefox-3.5

After upgrade to 9.10 and firefox 3.5, I noticed that on the some pages, the firefox would be freezed for a while(tens of seconds), then continue to work. At first I don't know what cause this, and suspect website's js. But at one time when freezing, firefox told me:

>A script on this page may be busy, or it may have stopped responding. You can stop the script now, or you can continue to see >if the script will complete.
>
>Script: file:///usr/lib/xulrunner-1.9.1.4/components/nsProxyAutoConfig.js:133

Then I know the reason. I am using autoproxy script in the company, then I tried one certain proxy and it work. So seems the following function is the root cause(I don't have this problem when using firefox 3.0):

129 // wrapper for resolving hostnames called by PAC file
130 function dnsResolve(host) {
131 host = XPCSafeJSObjectWrapper(host);
132 try {
133 return dns.resolve(host, 0).getNextAddrAsString();
134 } catch (e) {
135 return null;
136 }
137 }

So I believe there is some reasons that dns.resolve() didn't return quickly. But seems not due to my proxy server.

Thanks in advance to look into this.