Very Useful Rated 5 out of 5 stars
Regarding the next comment that this extension is a default firefox feature available at mycroft, this is not entirely true.
First of all, while there are thousands of search engines to choose from, it takes a lot of time and effort to peruse through mycroft's exhaustive list, and the added convenience and speed of "Add To Search Bar' alone is worth downloading.
Second of alone, not every search engine is
available via mycroft.
I wholeheartedly recommend this as a Must-Have.