Simple Translate does not work correctly

Steps to reproduce:

1. Install the extension from https://addons.mozilla.org/en-US/firefox/addon/simple-translate/
2. Highlight some text. Notice no translation button pops up.
3. (Only the toolbar icon works.)

Expected behavior:

1. When text is highlighted, a translation button pops up and the translation is displayed instantly.
2. Refer to https://addons.mozilla.org/en-US/firefox/addon/simple-translate/ for screenshots of expected behaviour.

Orion, OS version; hardware type:
Orion Version 0.99.109.1.3-beta (WebKit 613.1.12)
macOS 12.1
MacBookPro15,2