As a general rule installing ‘free’ toolbars into your browser, either on purpose or by accident, is a really bad idea. Browser toolbars are such close kin to viruses that most times it is hard to tell them apart. If you want your browser to become unreliable and begin to get somewhat tardy, and possibly downright slow, then just install a few toolbars—that’ll usually do the trick.
One of the problems with browser toolbars is they generally get installed by stealth. What happens is that you download some ‘useful’ utility or popular game that you want to use and then buried in one of the install screens somewhere is a tick-box to install ‘such-and-such’ toolbar. The tick-box will be pre-ticked by default and it is up to you to spot it on the 4th, or 5th, or 6th install screen and un-tick it before clicking on “Next”; otherwise the toolbar installs.
The following example from slashignore (here) shows a sample of some of these performance robbing stealth-installing toolbars.
The other problem with these pesky little browser toolbars is that they tend to be particularly tricky to remove—not all, but some. They generally do not have an uninstall option and they usually cannot be uninstalled via the Control Panel; and simply turning them off on the toolbar menu does not uninstall them—they are still there and running even if they cannot be seen on the browser.
So, the bottom line, don’t install those ‘free’ browser toolbars unless you know exactly what they are and you actually want them installed for a specific reason.