1) Did you already go to your Control Panel and uninstalled the following - Delta Chrome Toolbar, Delta toolbar, Yontoo, BrowserProtect, Mixi.DJ, and anything whose publisher is listed as Delta?Apparently, in my father's quest for free antivirus software (none of my doing), he acquired something called Delta Search. What it is, I have no idea, but it's hijacked Firefox and pops open every time I open a new tab, and even uninstalling it doesn't seem to have gotten rid of it. Any advice?
2) If yes, since you are a Firefox user, click the orange Firefox button in the upper left corner of the screen, click on Add-ons, go to Extensions, remove Delta Toolbar, Mixi.DJ and Yontoo extensions, and restart Firefox.
3) You likely have to also need an extension to reset your search engine properly. SearchReset should do the trick.