This add-on was the only reason that I sometimes had to switch to Chrome, because one of my apps has a very long form fields that I need to fill with dummy data and this add-on is the only one I found does the work with no issue. I got surprised when I saw it's available here on Firefox now.
Kudos to the developer.

Tested quite a few auto-fillers.. some don't work as claimed, some require tedious configuration, this one just works.
Thanks!