(Android) How can I point Firefox to a local file on SD card?

I have the latest Firefox 150.0b3. Android Firefox's bookmark management "leaves something to be desired". On the SD card, I created a "bookmarks" directory under "Documents" and uploaded a sample "index.html". So far...

• Plan A: I dove into the file structure and tapped on "index.html". I was presented with options to use OpenDocumentReader or Chrome or HTMLviewer. Firefox was not presented as an option
• Plan B: "I asked Mr. Google", and was told to try url

file:///sdcard/Documents/bookmarks/index.html

That didn't work

Any other ideas?