Good, but needs some tweaks Rated 4 out of 5 stars
I was reluctant to try this extension after reading about the author hard-coding his name into the menu (a practice which I find abhorrent regardless of whether it's done by an individual developer or by a large company). Fortunately this seems to have been removed and there are now only proper menu items displayed in the context menu. (See the author's screenshots).
On the whole I like this extension. While there are other similar extensions such as Context Search that work really well, I prefer the wording of the context menu on this particular extension. "Search With" makes perfect sense and it applies regardless of where you happen to be searching. Whereas other extensions that use menu names such as "Search Web for" does not make always sense (for example when searching your own bookmarks). Also, because 'Search with' does not make the selected text part of the displayed context menu name, you don't get constantly varying width menus or truncated text displayed (like you do with other extensions such as Context Search). This problem does not occur with the 'Search with' extension because the menu item is static and it always just says "Search with". This is nice and consistent and predictable.
One thing that I don't like about 'Search With' is that it displays the context menu even when no text has been selected. This is pointless because even if you select a sub-menu item, no results can be given because no text has been selected. Instead you have to manually type in the search term (which you could have done using Firefox's search bar in the first place). I would therefore like to see the removal of the 'Search with' menu item from the context menu when no text is currently selected. Or, failing that, there should at least be an option to only display the 'Search with' menu entry when some text has been selected somewhere.
It would also be good if there were options to individually hide the Address bar, All Services and Manage Services menu entries for a cleaner looking context menu. The "I'm feeling lucky" search that gets done when using the Address bar is of limited use, so not everybody will want it visible and cluttering up their menu. Likewise, the All services is not going to be used by everybody, especially if you have a lot of engines (it would open up too much). So it would be nice to have an option to hide that particular menu item too. The Manage Services option is obviously important to most people (except those who only ever use the default engines), but Manage Services can also be accessed via the Options button for the Search With extension on Firefox's Addons page. Therefore the Manage Services entry can also be made optional (for those who don't want or need it) because there is still a means of accessing it even when the menu item is not shown.