Ask HN: Why is creating a custom Firefox search engine so difficult?

This simple issue has been bothering me for a couple of years now and I've never been able to find anything resembling a solution - I like having control of the search engine options in my browser and want to add custom searches. Chrome maintains the tradition of allowing a URL string with some predefined parameters. Firefox, on the other hand, requires some sort of custom XML mess with no clear and simple way to create a custom search engine from scratch. I see some minimal benefits, such as the ability to pair an icon with a search engine and the ability to use short names, but I just want to type a search into the search bar and have it send me to a custom search of my choice.

Is this shift to OpenSearch format mostly to prevent people from doing away with Mozilla's referral codes in the search strings? I just can't see any good reason this must be so complicated with so little customizability.

To be completely clear, I want to add the equivalent of "https://<customsearchengine>.com/q={searchparam}" to replace any/all of the built-in search options and am not currently looking for other solutions, such as websites with lists of predefined search engine queries. I also don't want to be dependent on finding some online service to do this for me. Any suggestions or feedback on why this process has become so complicated?