How to add a search engine when using the unified address & search bar in FF 57?
FF57 offers the option to also use the address bar also for searching, i.e. eliminating the dedicated search bar (or field). When doing so I miss the possibility to add a search engine with one click when visiting a site with search functionality. See https://support.cdn.mozilla.net/media/uploads/gallery/images/2015-08-04-10-26-53-ba9bf0.png to understand what i mean.
Alla svar (2)
You would have to use the search bar that gets a green plus icon attached when the website offers a search engine like this page. You can move the search bar to the overflow area if you do not want to have it ivsible on the Navigation Toolbar.
There is discussion in Bugzilla (bug tracking system) about how to add this to the address bar somehow, but it isn't going to happen in Firefox 57.
In an earlier thread, I posted a snippet of script you could save as a bookmarklet to check whether the page is advertising a search plugin and install it. But it doesn't get a "+" on the button, so you would just need to check if it's a site you think might be useful for searching in the future.
See: How to install a search plugin offered by the current page?