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Martin Klier

usn-it.de

Blocking network loopback slows down firefox extremely

My newly installed Firefox web browser (versions 2 and 3, does not matter) was deadly slow. I don’t mean the display of web sites, no, I am talking about pulldown-menus or opening tabs. (For example, bookmarks folder opens within 6 long seconds.) Several hours I was not able to tell why it acts that way. But now, I found out:

The system is protected with a host firewall. Ruleset:

iptables -t filter -F
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT
#mark
iptables -t filter -A INPUT -m state \
   --state ESTABLISHED,RELATED -j ACCEPT
iptables -t filter -A INPUT -j REJECT \
   --reject-with icmp-port-unreachable

But inserting this:

# Firefox seems to do stuff over loopback, 
# it's deadly slow without that setting
iptables -t filter -A INPUT -i lo -j ACCEPT

at “#mark” makes it work fast as usual.

Tell me, why are they doing ther menu communication via loopback network socket?

Just in case you might wonder, too.
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