FF prompting to save Navigator credentials

I've always used Chrome for Navigator, logged on as myself. It doesn't
let me log on as two different users, so I've always just used iNav when I
need QSECOFR. The "writing is on the wall" for iNav, so I'm trying to
transition away. I'm now trying to use Firefox when I need Navigator as
QSECOFR. I can't seem to get Firefox to stop prompting me every time to
save my credentials. I choose the "Never save" option every time, but it
still keeps doing it.

Has anyone seen this? Any suggestions?

TIA