Explanation

Opera doesn't support Firefox Smart Keywords. When you import Firefox bookmarks into Opera, you lose the ability to use any bookmarks with a "%s" in the URL to search. This page changes all the smart keyword bookmarks into the search.ini Search Engine format so they'll work in Opera. Tested with Opera 10.62.

Instructions

1. Export your Firefox bookmarks as HTML
2. Paste the resulting HTML in the top text area
3. Open %USER_PROFILE%\Application Data\Opera\Opera\search.ini in a text editor and scroll to the end
4. Back up search.ini just in case
5. Enter what the next search engine number should be in the Starting Search Engine Number field
6. Hit convert (each bookmark with a "%s" in the URL will result in a search engine entry)
7. Paste the contents of the lower text area at the end of search.ini
8. Start Opera, hit Ctrl-F12 and go to the Search tab to see the new Search Engines

Note:

For some reason the search engines added this way don't sync through Opera Link unless you modify them and save them through the Opera interface. I'm looking into why that is.