speed of surfing with router drops down

[shbk]

speed of surfing with router drops down in ubuntu.
i have ubuntu. computer is connected to internet via router dlink dir-615 via pppoe(russian dual access). at the second computer in lan, where xp is installed , all works fine. when i download xp on the first computer (my) ,all works fine too. so ,i think what router works well and problem is in linux's setups.

i read about mtu and people think what it can be a problem. router and ubuntu have a same Mtu.
torrents, loading from ftp servers works right.
loopback confuses me. i didn't see her in xp. but i don't sure.
what do you think about this?

this is my ifconfig:
eth0 Link encap:Ethernet HWaddr 00:24:54:43:62:fe
inet addr:192.168.10.101 Bcast:192.168.10.255 Mask:255.255.255.0
inet6 addr: fe80::224:54ff:fe43:62fe/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1492 Metric:1
RX packets:265407 errors:0 dropped:0 overruns:0 frame:0
TX packets:186054 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:21431966 (21.4 MB) TX bytes:617153757 (617.1 MB)
Interrupt:19

lo Link encap:Локальная петля (Loopback)
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:74 errors:0 dropped:0 overruns:0 frame:0
TX packets:74 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:4236 (4.2 KB) TX bytes:4236 (4.2 KB)

[shbk]

all was very simple. i think what big cache of browser is well, but very big cache is better. but i overdo. i set size of cache 1.5gb. and as result my surfing had become very slow. i think cause in that browser checked current loading page with cache. when i decreased size of cache to 50 mb speed is fast.