firefox-mv3: RequestDOM fails with TypeError, z is undefined

I am trying to test this extension on Firefox. Using either firefox-mv2 or firefox-mv3 targets, I get the following failure:

Uncaught (in promise) TypeError: can't access property "message", resp is undefined
    sendToBot popup.tsx:348
    handleSubmit popup.tsx:381
    nextTick popup.tsx:16
    setTimeout handler*nextTick popup.tsx:15
    handleSubmit popup.tsx:381
    React 23
    Vd1oM popup.tsx:14
    Vd1oM popup.tsx:8
    newRequire popup.df1d3259.js:71
    <anonymous> popup.df1d3259.js:122
    <anonymous> popup.df1d3259.js:145
popup.tsx:348:8

I'm guessing the root cause is somewhere earlier:

Firefox can’t establish a connection to the server at ws://localhost:1815/. runtime-dd9c566522733cc9.js:1:2820

🟠 WARN   | [plasmo/parcel-runtime]: Connection to the HMR server is closed for /workspaces/browser-friend/.plasmo/static/background/index.ts runtime-dd9c566522733cc9.js:1:362

XHR GET http://localhost:1815/ [HTTP/1.1 404 Not Found 271ms]

Uncaught (in promise) TypeError: can't access property "some", t is undefined
    d runtime-dd9c566522733cc9.js:5
    InWiR runtime-dd9c566522733cc9.js:5
    InWiR runtime-dd9c566522733cc9.js:5
    newRequire background.aeab42a0.js:71
    <anonymous> background.aeab42a0.js:122
    <anonymous> background.aeab42a0.js:145
runtime-dd9c566522733cc9.js:5:542

Is Firefox not supported in Plasmo? The documentation seems to suggest it is, but there seem to be a ton of ... warts I guess is the word ... that imply otherwise.

cantino / browser-friend

firefox-mv3: RequestDOM fails with TypeError, z is undefined #2