Help with firefox?

[Sigve]

When i open a new tab, this crap comes up: http://search.snapdo.com/?st=nt&q= instead of the about:newtab page. The other day i was browsing, and suddenly the browser restarted, and when i opened it again, much crap had happened to the home page and newtab page and everything... How do i change it back to the normal new tab page? I cant find any addons that has anything with snap.do to do or anything.

I also want the about:newtab page as home page. So when i change my home page to about:newtab, it works, but when i restart the computer again, the homepage is google...

The last thing, why does the default search engine on firefox automatically change to yahoo?
When i change it to google, it is yahoo again when i reopen the browser.. ToT
http://gyazo.com/68fc4ee6ab4f365bc20c6479c62e2005