Okay I've been having this issue ever since I've installed FC4 on my computer. the internet is always slow on my Linux, but fine on all my Windows. I've noticed that pages take about 10 to 40 seconds to load using Firefox while posting on forums, some registrations, and some webmail will never be sent (times out). I have to log on to my Windows to do this and it's very annoying!

However, I've noticed that downloading is fine. Konqueror is unbarebly slow, Firefox is almost unmanable, and Opera is around a 56K speed on most pages. Also there isn't any memory problem.

I have a basic LAN cable connected to my D-Link router to a 2WIRE modem. I've tried to figure out the issue by contacting my internet provider, SBC Global, and they say it's a problem with Linux. Yah BS! Thanks to anyone who can help!

Could be a DNS problem. Check your /etc/resolv.conf and see if the isp DNS addresses are there. To speed up DNS resolution you could also use the router address in resolv.conf because most routers have dns-caching.
Also check the lan stats for errors and collisions using ifconfig from the command line.

I don't know if this will help, but one thing that I noticed was this; If I opened up a console window and pinged www.google.com it would return the responses alomst instantly, but if I tried to hit google from Firefox it was really slow, and sometimes couldn't resolve the web site name. After searching a bit and checking different settings for DNS I found that they were all fine, if you are using Firefox and it seems slow, but you can ping fine from the console, try turning of IP6 address resolution in Firefox, I did this and it fixed my slow connection problem. To turn of IP6 resolution simply open up Firefox and type in 'about:config' in the address bar. When the page loads, at the top of the window in the Filter field, type in 'dns', the first line should be "network.dns.disableIPv6", it's defaulted to a value of false, simply double-click on that line and it will change the value to true. Close your browser, launch it again and hope that it fixes your problem like it did mine.

Hope it helps

-Jonathon