Option 1
Speed up FireFox:
1. Type "about
:config" in the address field (without quotes).
2. Set the value of network.http.pipelining to "true".
3. Set the value of network.http.pipelining.maxrequests to "100".
4. Set the value of network.http.proxy.pipelining to "true"
5. Set the value of nglayout.initialpaint.delay to "0"
Option 2 (nearly identical to Option 1)
Try these settings:
http://img208.exs.cx/img208/9720/aboutconfig4yk.jpg
Option 3
Another way to speed up Firefox (especially for broadband):
1. Type "about
:config" in the address field (without quotes).
2. Right-click anywhere and select New > Integer.
3. Name it "nglayout.initialpaint.delay" and set its value to "0". The value is the amount of time the browser waits before it acts on information it receives.
Option 4
I've heard good things about Firefox Preloader, however, I haven't tested it. If anyone does, please let me know if you see a difference.
Here's the link:
https://sourceforge.net/projects/ffpreloader/
NOTE: When you change the settings you will need to restart Firefox.
Edit:
Found other ways to speed up Firefox. I ganked it from another forum.
1. Type "about
:config" into the address bar and hit enter. Scroll down and look for the following entries:
network.http.pipelining
network.http.proxy.pipelining
network.http.pipelining.maxrequests
Normally the browser will make one request to a web page at a time. When you enable pipelining it will make several at once, which really speeds up page loading.
2. Alter the entries as follows:
Set "network.http.pipelining" to "true"
Set "network.http.proxy.pipelining" to "true"
Set "network.http.pipelining.maxrequests" to some number like 30. This means it will make 30 requests at once.
3. Lastly right-click anywhere and select New-> Integer. Name it "nglayout.initialpaint.delay" and set its value to "0". This value is the amount of time the browser waits before it acts on information it recieves.
Another tweak:
First, install
ChromEdit (
http://www.extensionsmirror.nl/index.php?showtopic=21) extension. It make it easier to edit user files.
Now, run Firefox, go to Tools > Edit User Files, click
user.js tab.
Insert the following texts based on your PC speed and internet connection.
Common to all configurations
These are the settings that seem to be common to all configuration files regardless of connection speed or computer speed with a couple of additions - plugin paths can be found with about

lugins and the bookmark menu delay is turned off.
CODE
user_pref("network.http.pipelining", true);
user_pref("network.http.proxy.pipelining", true);
user_pref("network.http.pipelining.maxrequests", 8);
user_pref("content.notify.backoffcount", 5);
user_pref("plugin.expose_full_path", true);
user_pref("ui.submenuDelay", 0);
Fast Computer Fast Connection
CODE
user_pref("content.interrupt.parsing", true);
user_pref("content.max.tokenizing.time", 2250000);
user_pref("content.notify.interval", 750000);
user_pref("content.notify.ontimer", true);
user_pref("content.switch.threshold", 750000);
user_pref("nglayout.initialpaint.delay", 0);
user_pref("network.http.max-connections", 30);
user_pref("network.http.max-connections-per-server", 16);
user_pref("network.http.max-persistent-connections-per-proxy", 16);
user_pref("network.http.max-persistent-connections-per-server", 8);
user_pref("browser.cache.memory.capacity", 65536);
A couple settings of note - Firefox is allocated 4096 KB of memory by default and in this configuration we give it roughly 65MB as denoted by the last line. This can be changed according to what is used.
Fast Computer, Slower Connection
This configuration is more suited to people without ultra fast connections. We are not talking about dial up connections but slower DSL / Cable connections.
CODE
user_pref("content.max.tokenizing.time", 2250000);
user_pref("content.notify.interval", 750000);
user_pref("content.notify.ontimer", true);
user_pref("content.switch.threshold", 750000);
user_pref("network.http.max-connections", 48);
user_pref("network.http.max-connections-per-server", 16);
user_pref("network.http.max-persistent-connections-per-proxy", 16);
user_pref("network.http.max-persistent-connections-per-server", 8);
user_pref("nglayout.initialpaint.delay", 0);
user_pref("browser.cache.memory.capacity", 65536);
Fast Computer, Slow Connection
CODE
user_pref("browser.xul.error_pages.enabled", true);
user_pref("content.interrupt.parsing", true);
user_pref("content.max.tokenizing.time", 3000000);
user_pref("content.maxtextrun", 8191);
user_pref("content.notify.interval", 750000);
user_pref("content.notify.ontimer", true);
user_pref("content.switch.threshold", 750000);
user_pref("network.http.max-connections", 32);
user_pref("network.http.max-connections-per-server", 8);
user_pref("network.http.max-persistent-connections-per-proxy", 8);
user_pref("network.http.max-persistent-connections-per-server", 4);
user_pref("nglayout.initialpaint.delay", 0);
user_pref("browser.cache.memory.capacity", 65536);
Slow Computer, Fast Connection
CODE
user_pref("content.max.tokenizing.time", 3000000);
user_pref("content.notify.backoffcount", 5);
user_pref("content.notify.interval", 1000000);
user_pref("content.notify.ontimer", true);
user_pref("content.switch.threshold", 1000000);
user_pref("content.maxtextrun", 4095);
user_pref("nglayout.initialpaint.delay", 1000);
user_pref("network.http.max-connections", 48);
user_pref("network.http.max-connections-per-server", 16);
user_pref("network.http.max-persistent-connections-per-proxy", 16);
user_pref("network.http.max-persistent-connections-per-server", 8);
user_pref("dom.disable_window_status_change", true);
One of the changes made for this particular configuration is the final line where the status bar is disabled for changing web pages to save processor time.
Slow Computer, Slow Connection
We have entered the doldrums of the dial-up user
CODE
user_pref("content.max.tokenizing.time", 2250000);
user_pref("content.notify.interval", 750000);
user_pref("content.notify.ontimer", true);
user_pref("content.switch.threshold", 750000);
user_pref("nglayout.initialpaint.delay", 750);
user_pref("network.http.max-connections", 32);
user_pref("network.http.max-connections-per-server", 8);
user_pref("network.http.max-persistent-connections-per-proxy", 8);
user_pref("network.http.max-persistent-connections-per-server", 4);
user_pref("dom.disable_window_status_change", true);