must be default in firefox!! thanks, really only the way to add missed search engines! <3
Here is my answer:
@How to add a custom search engine to Firefox?@

https://superuser.com/questions/7327/how-to-add-a-custom-search-engine-to-firefox/1474187#1474187

and here as well:
@Firefox: add Google search engine - why no such option in search/address bar?@
https://superuser.com/a/1549586/230571

添加时出现这样的提示：SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

It does what it says, and requests no unnecessary permissions. Excellent add-on!

Works like a charm.

works wonderfully, though some UI decisions (like changing %s to {placeholder} when switching get to post) are questionable

Tom is the man!
This allowes me to configure my most used engines (ling.pl, allegro.pl) which otherwise would not be supported.
Kudos!

Does exactly what it says. Also, it's the only extension from those I tried that actually works with Firefox 74!

Works great. Just find what the search text should be, click the link, substitute the term(s) with %s, add it, and you're good to go.

If you want keywords for your search engine as I do, just go to "Search" and add a keyword (or letter as in my case) and it's easy peasy lemon squeezy and your searching for an easy to add and modify search engine manipulation is over.

Working as intended! Does this addon have an android version with such functions (edit of search field suffixes etc.)?

It does what it is supposed to do. Perfect!

Works perfect. Just make a test search with the search engine you want to add and at the url replace your search term after the = with %s. Use a favicon generator in the web for an icon

Righteous. Instruction is clear & concise so it feels effortless to understand and use. Always works without issue. Thanks so much!