IE8 & Firefox require an add-on to be installed for each search provider which internally uses a standard XML-based OpenSearch Description File. In contrast, Opera lets you quickly configure a search provider yourself for any any site that provides it. Let's see how to search StackOverflow, the programming Q & A site, right from the Opera browser.
1. Go to Tools > Preferences & select the Search tab in the dialog box that opens up. It contains a list of search providers like Google that are already added by default.
Name: Stack Overflow
Keyword: so
Address: http://stackoverflow.com/search?q=%s
3. Click on the OK button to save these settings & after that you will notice Stack Overflow as a search engine option for the search box.
Instead of using the search box, you can also search from the address bar by typing the keyword so followed by your search query to look up StackOverlow specifically. Example - so jquery
If you wish to exclude certain sites from being included in the results displayed by popular search engines like Bing & Google, you can edit search settings to restrict sites using the site: operator. For example, to exclude results from the domain example.com when you search Google from the Opera search box, edit the address in the Search preference for this search engine to look something this -
http://www.google.com/search?q=%s+-site:example.com