I recently had to reinstall Firefox and had both regular and Developer editions on my system. Before reinstalling the standard version, I had the Developer version as a selection in the Preview in Browser. Since the reinstall, however, I only have the standard Firefox.
I couldn’t track down any setting to change this, as I would much rather use Developer edition when previewing rather than standard. There wasn’t anything helpful on the Firefox site, either, so hopefully I can get some help here!
Unfortunately, I have zero control over that, as the ability to do so is locked down administratively. What was odd was that at one point, it was a choice until I installed the update to the standard edition. I might just try using just the developer edition, since there’s little difference anyway.