Often installing free software it happens you could not take care about other software will be installed, generally they are browser addons that put toolbars and change default homepage address.
Talking specifically about Firefox browser (under Windows) there are some methods to fully remove them.
Check if the addon is in Windows installations and uninstall, install an adware removal tool (eg. Spybot Search and Destroy) and do a scan, the tool can find other elements to remove.
In this way the most number of addons/adware should be removed but if it isn’t enough you can do some manual actions.
Thanks to the suggestions of Remove a toolbar that has taken over your Firefox search or home page article you can remove the easily the toolbar, you can reset the Firefox preferences to initial state by pressing the Refresh Firefox button.
If this doesn’t work you can reset browser settings from Help menu and select Restart with Add-ons Disabled… and check to reset all user preferences to defaults and Restore default search engines, apply changes and restart (see the screen below)