Your Internet may be up to 300 times slower than it should just because you have toolbars such as Skype installed on your Firefox or other internet browser. The 2011 version of the Skype Toolbar was one of the top crashers of Mozilla Firefox 3.6.
To fix this, you can uninstall the Skype Toolbar from the Add or Remove Programs in the Windows > Control Panel > Programs and features, or disable it by open Firefox, go to Tools > Add-ons > Extensions, find the Skype extension for Firefox and click Disable.
Note that removing the toolbar does not remove Skype itself. The Toolbar is a bundle that allows you to initiate phone calls directly from web pages by clicking on highlighted phone numbers, which will launch Skype to dial the number. If you do not use that feature, you can uninstall toolbar.
You may uninstall other extensions in Firefox and other browsers such as Chrome and Safari on Mac. Extensions could be installed unintentionally as bundles by free programs you installed once.