It seems this problem is back.
After setting up Firefox Developer's Edition v70, then moving it to a different path, the following happens:
1. It loses the set Theme and reverts to the default Dark Theme.
2. Add-Ons no longer work. Some of them can be made to refunction by disabling then re-enabling them.
Is there a workaround, or do we need to wait for the next version of the Firefox Developer loader app?