Hi, as has been already said, there are various options, in particular the side can add one, or you can add a keyword.
We are working towards allowing custom engines in bug 1650874 and its dependencies.
(In reply to Dan Dascalescu from comment #1)
Went to about:config. I'm surprised how opaque search is:
- where are the search URLs for each search engine?
The default engines are product supplied, and we don't allow changing of those URLs. Most people don't need to, and you have other options for changing to different search engines.
- why is Yahoo! even listed, let alone as #1, when I've remove it?
Likewise, that's an obsolete preference, and the default search engines are not changeable. If you remove them, you effectively hide them and they will not be used no activated.
- what's up with "browser.search.param.yahoo-fr"? This is a US English installation. I expect to be able to remove that setting, but there's no trash bin icon next to it.
This is are also an obsolete default preferences set by your Linux Mint distribution. You cannot remove default preferences, you can change them, but they may / may not take affect. Generally about:config is not intended to let you change absolutely anything in the browser.
I'm resolving this as invalid, as I think this is a misplaced support request, and the main issue is already covered by existing bugs.