Why aren't the settings accessible through the firefox extension manager? Why only through clicking through the toolbar button?

Also, what is the correct format for 'ffmpeg path'?
To the executable? (yes, through trial & error)
To bin dir?
To overall ffmpeg dir?

What is the correct format for 'save merged files in'?
Quotes surrounding the dir or no? (no, more trial & error)
'\' at the end or no? (also no)
Why only 'merged files'? How can I set the save directory for all downloads?

'Consider OPUS' seems to fetch OPUS for MP4 grabs as-well even though the option makes it sound like it's for WEBM fetches only.

Where have the options to remove WEBM, OGG etc options from the download panel gone?