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It's never been a better time to switch to Firefox
(www.androidpolice.com)
This is a most excellent place for technology news and articles.
Firefox doesn't explain how to do this at all, but it is possible. Make a bookmark with the URL you want, and set the keyword to whatever symbol you want ti start it with.
For example,
Name: Scryfall (or whatever you want)
URL: https://scryfall.com/search?q=%s&unique=cards&as=grid&order=name
Keyword: s
Then type "s Birds of Paradise" to get the result you want.
I did the same with Reddit and it worked on my end. If it doesn't work for you I'd be happy to help you figure it out.
It's also possible on mobile, and it's actually even easier: Settings>Search>Default Search Engine>Add Search Engine. Then you can type your search and choose the engine from a dropdown menu.
This is the way. The dude in the comment above the one I am replying to described a different way where you have to change the config, which would be neccesary to do on every new installation. Via the bookmarks/shortcuts method you will have the BANG Search on every new installation just by importing your bookmarks - or if you use an firefox account with synchronisation you will already have it with your login.
Be advised that duckduckgo has already some predefined BANG Searches, that you can use without having to change anything. Just type in the search bar: