When I start to type something, the add-on works as intended, but when I press enter, is opens a new tab, with nothing in it.
Switching search engines with arrows works, and when I press the search engine icon, it open a new tab with the request on the right search engine.
Browser: Firefox 99.0
Add-on version: 1.0.1
Note: I have this issue without doing any configuration to the add-on.