This functionality is (sort of) already possible in firefox (and possibly other browsers) and I use them quite often, the only problem is that managing them is not as straight forward.
An example bookmark which allows you to search on npm:
I’ve noticed this as well. That is why I’ve started scraping those agency websites and send an email whenever a new listing matching my criteria came online. I even made a tool out of it for others to use [1] (it currently crawls around 50 sites).
It generates functions. Though not with a “$@“ at the end, so passing additional arguments at this moment is not supported. I also run a syntax check before the function is added to the file.