The extension functionality is A-OK, solid 5/5. It's the implementation that kills it usefulness, and barely scrapes 0/5. I could go into the negative score numbers, but boy, where I would've stopped then...

I had to uninstall the extension because it throws its trash around all over the browser. It injects a humongous CSS stylesheet, 115KB(!) in size, into *every single open tab*, regardless of DeepL translation being ever used. I estimated that I used the selection translation pop-up at about one in every 500 to 1000 pages. This is a truly humongous waste of resources. The stylesheet contains 734 selectors, 2999 property settings and two @media width breakpoints. You'd have a hard time convincing me that this is a bare minimum necessary to display a simple pop-up box…

And then, in any case, a sensibly written extension would have delayed loading its CSS until it is actually needed, i.e. until it actually displays something. And load it into a sandbox, so that it's gone when the pop-up is closed: come think of it, DOM shadow roots were invented for a reason, and scoping resources in time was one of the two major ones. Now, the funny part, albeit not ha-ha funny: the extension does in fact use a shadow root for the pop-up, and… yes, you guessed it, loads another copy of its juggernaut CSS sheet into it. Why it also stuffs all this useless CSS everywhere it only can is beyond me, but loading the CPU with the browser's failing to match the extra 750 selectors every time the layout is recomputed—and "responsive" layouts on dynamically changing pages have to be deeply recomputed often!—isn't something I can use. I have better ways to waste my CPU than this extension.

As soon as the issue is fixed, I'm upgrading my rating to 5/5 not thinking twice. I hope that this is just an oversight, a bad design decision that could be soon reassessed and undone.