On every search the browser gives the same site (bol.com)
Whatever I give as a search the browser gives back the same page of a company (i.c. bol.com). I can't get rid of this inspite of de-installing and re-installing. It looks like a kind of an infection.
You may have ad / mal-ware. Further information can be found in the Troubleshoot Firefox issues caused by malware article.
Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.