Another technique using Firefox and Windows is to enter" about:addons " in the web address block at the top of any Firefox page. You will get a page that will allow you to select which add-ons you want to run automatically and which you will want to operate only when you allow it. There will be 5 choices on the left bar.
Get Addons
Extensions
Appearance
Plugins
Services
Extensions and Services will be the ones you need to go to. In Extensions you'll find things like Avast (antivirus), Dashlane (password Manager), AdBlock, or others in this category. On the right will be a series of blocks that allow you to activate, deactivate or sometimes delete these additions.
On the left bar clicking "Plugins" will get you to things like Acrobat for Firefox, Shockwave Flash, Google Earth Plugin, Java, and Google Update and others. There will be boxes on the right where you can select if these additions are to run unrestricted, or only when you let them, or never. This way when a video that uses Flash comes up in your browser it will not load until you allow it to by clicking in a pop up box to allow it.
You can play around on the Add-ons manager page and find a lot of other neat things to add or delete, but this section makes controlling what add-ons and other junk gets added to your machine.
It's also an easy way to check and see if your add-ons and extensions are up to date and to find new ones that may help your browsing experience. But most of all it'll tell you what you really have on your browser that you don't want and may be slowing you down a great deal.