What is a Browser Add-On
Browser add-ons or plug-ins are add features(software which enhances another application) to the web browser.
For example you want feature in your browser backup and synchronize favorites accross other computers use a free add-on xmarks from http://download.xmarks.com/download/ie.
Where i can see the add-on?
In Internet explorer from Tools > Manage add-on can see the enabled/disabled add-ons
Some times add-ons cause problems to load the internet explorer or some times it will hang.For such conditions you can disable the add-ons which causing problems.
when you are not able to move to tools while IE hungs try to open from run window using command inetcpl.cpl it will open the window.
For mozilla add/remove add-ons from tools add-on.
For Chrome click on settings and then extensions.
Ad-on Galery site for Internet Explorer
Read more about IE Add-on from