Not necessarily. Developer is the beta channel, after all, so many of us use Firefox stable as our primary. I use my various PortableApps.com packages to run separate channels without impacting each other for testing sites.
I use Developer as my only browser. Never had any issues. It's not a buggy alpha version or something.
Even FF Nightly works perfectly well as a day to day browser for me. And I use it all day every day.
Nightly is surprisingly stable. In my past few years of using it, there have only been a few days when it has been unusable. On those days I just used Chrome. The e10s transition was pretty rough. It was common for every tab to crash at once, and sometimes there were long delays for tabs to paint when switching.