I noticed the following unwanted browser extensions in Firefox: Searchme, Slick Savings, Amazon Shopping Assistant, and Ebay Shopping Assistant. Turns out these are essentially malware that effected Firefox, Safari, and Chrome on my Mac. They're made by a supposedly legitimate company called Spigot, Inc.
While searching for an effective means of virus removal I found this link www.thesafemac.com/arg-spigot/
which gives detailed instructions how to do so.