My new laptop came with “AVG Secure Search” as the default engine and it was pretty annoying. Typing a query in the addressbar and hitting enter would throw up AVG’s SERP. Here’s how to change it:
In firefox’s addressbar, type about:config
In the filter bar, copy paste this browser.search.defaultenginename

Double click the entry and change it to the Search engine of your choice (It must be installed and the name should match that of an existing one)
For changing the default Address Bar Search Engine, you have to follow a similar method: in about:config filter, type in keyword.url

Type in http://www.google.com/search?ie=UTF-8&q= (Google default search) to make Google as your default addressbar search engine.
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