Firefox started out as a lightweight customisable browser which offered better performance than IE. Over the years it has steadily morphed into a piece of bloatware with frequent updates that often break your existing add-ons, and a lower performance than the lates IE versions.
Chrome is still an efficient and reasonably lightweight browser which is occasionally and unobtrusively updated.
To replace Chrome with FF just because you have installed a trojan makes no sense.
There are instructions for removing delta-search here:
http://malwaretips.com/blogs/delta-toolbar-virus/