Neat, I kept thinking there should be a way to add keywords to that list and now I know how to do it (execept for some reason you can only add a new engine with a keyword there and not add a keyword to an existing engine :( ). I use mozlz4 and aeson-pretty to look at the search.json.mozlz4 file.
To be fair you can also just right click on the URL bar when on a page that advertises having a search and click Add <name of search>. Or if you want to search by keyword you can right click on most search boxes and click "add a keyword for this search". Mycroft Project has a bunch of random search engines ready to add to Firefox (via right clicking on the URL bar when on the search entry page):
If you use more than one search engine, I like the Right Click Search addon to be able to search highlighted text with multiple engines easily (unfortunately not monitored by Mozilla but you can look over the code before installing and turn off updates since it is quite simple and requires no permissions):
https://github.com/jusw85/mozlz4
https://github.com/informatikr/aeson-pretty
To be fair you can also just right click on the URL bar when on a page that advertises having a search and click Add <name of search>. Or if you want to search by keyword you can right click on most search boxes and click "add a keyword for this search". Mycroft Project has a bunch of random search engines ready to add to Firefox (via right clicking on the URL bar when on the search entry page):
https://mycroftproject.com/
If you use more than one search engine, I like the Right Click Search addon to be able to search highlighted text with multiple engines easily (unfortunately not monitored by Mozilla but you can look over the code before installing and turn off updates since it is quite simple and requires no permissions):
https://addons.mozilla.org/en-US/firefox/addon/right-click- search/
The most privacy friendly way to search is to search the site you want to end up on when you know what site that is and they have a usable search.
For general search engines, I suggest giving Metager a try, it is a non-profit metasearch.
https://metager.org/