FOSS. It works in Mozilla Firefox 133.0 (64-bit) under Windows 10, but you have to enter everything manually, not visually, without using the keyboard, as is implemented in similar add-ons. Some sites are incompatible with such a search due to the replacement of the space character (%20) with the “+” character.

Upd. The add-on no longer works: "SyntaxError: JSON.parse: unexpected end of data at line 1 column 1 of the JSON data".