Using the TWebLocalBinaryFile to save a recording created with TWebMediaCapture does on work in Firefox. Get the following error in the JavaScript. javascript error TypeError: window.showSaveFilePicker is not a function on code line const handle = await window.showSaveFilePicker(jo). Apparently that function does not exist in firefox.
The underlying used JavaScript API createWritable() method is part of the File System Access API, which Firefox doesn't fully support. This createWritable() API is currently only available in Chromium-based browsers (Chrome, Edge, Opera, etc.).
You might try this extension on FireFox