Monty,
I would hazard a guess that you have alot of background processes running you are not aware of, including addons for your browser.
You didnt mention your operating system, but for vista/win 7
Click on the start button and in the search bar at the bottom type msconfig.exe and press enter.
A window will open, and you should click on the tab called startup.
I will imagine you will have alot of things here ticked? these are all the things which switch start by themselves when you switch your computer on.. as a rule you could untick absolutely everything here and you wouldnt break anything. you may find however that some things stop working and you would have to retick them in order for them to work as expected, so not a big deal if you accidentally untick the wrong one. There are a lot of them, wasn't sure which one to uncheck. I'll try all.
To give you a guide, in my list all i have is my anti virus, and my firewall. we obviously want them to switch on when i start my pc.
Read through yours one by one and if you are not sure what they are, google them to find out. remember things like adobe auto updater, and printer diagnostics and things like that can be unticked without causing you to lose any functionality on your PC. the less things ticked the better... be ruthless. I have 3 items.. see if you can beat it.
This is just one step, but its a very good one. Click on OK, and reboot your PC.. when its rebooted a ms configuration window will appear telling you , you have made changes to your computer. put a tick in the box saying dont show this again, and give your pc a spin.. think you will find its much better.
After this, check browser addons and tool bars which are in firefox... remove all of them if you dont use any of them...only one or two, if any