Open the Firefox browser and type about:config in the address bar. Accept the warning and continue.

Backup prefs.js. If something goes wrong, we can restore it by replacing the corrupted file. In Windows XP you can find it under C:\Documents and Settings\{your username}\ApplicationData\Mozilla\Firefox\Profiles\{profilename-with-some-string}.default\prefs.js

If it is not getting restored via the backup prefs.js file, we can exit Firefox and issue the command firefox -safe-mode to bring up the Firefox Safe Mode screen. Select Reset All User Preferences To Firefox Defaults.

Speed up Firefox

Search for the following entries and give values as shown below.

network.http.max-connections = 96
network.http.max-connections-per-server =32
network.http.max-persistent-connections-per-proxy =16
network.http.max-persistent-connections-per-server = 10
network.http.pipelining = true
network.http.pipelining.maxrequests = 8 
network.http.proxy.pipelining = true
network.http.request.max-start-delay = 0

Experiment with other values too. Now right click and choose New > Integer. Give the name nglayout.initialpaint.delay and set the Integer value as 0. This value is the amount of time the browser waits before it acts on information it receives.

Disable extension install delay

security.dialog_enable_delay = 0

Default is 2000.

Spell check in all fields

layout.spellcheckDefault = 2

By default, Firefox checks spelling only in multi-line text boxes.