There's a big chance that the cause of your browser running slow is actually because your internet connection is pretty bad. I'm having this problem as well, even though my laptop is only a year old. I've found that changing my preferenced DNS server to 8.8.8.8 has slightly increased speed. You can do this by right clicking on your connection, then choosing status. There you go to properties and then to the Internet Protocol version 4 properties (it might be worded a bit differently, my OS language isn't English). Moving you computer closer to your router or using a wired instead of a wireless connection will help with this as well.
If you think that it is in fact your slow computer that causes the problems you should uninstall as many toolbars, extensions, add-ons, etc. as possible. Also, if you don't tend to have many tabs open at the same time you should use Chrome as browser, otherwise Firefox is better.