While you can expand your arsenal of search engines by installing more search plug-ins, why not just create your own search plug-ins quick in easy just through a few clicks on a search page. OpenSearchFox lets you do just that. Really nifty if you’d want to create your own.
Say you’d like to use K-Fed’s search engine (just an example, like you’d really use this crap), all you have to do is right-click on the input form and click on the “Add OpenSearch plug-in” option. It even captures the favicon for reference.
Best application? Use with all those fancy-schmancy search options. Create one for Google Images and Google Code. No more trying to use those complex search modifiers. Do all your searching with Firefox’s search bar.