Extensions breakage is not the same as low browser stability though.
Keeping things working is not solely the task of mozilla devs, extension developers have to do their part too.
Sometimes it's easy easy as toggling off some experimental feature or installing a beta build of that extension.
At other times you'll have to report a bug yourself.
And sometimes extensions just die because they're unmaintained. It happens eventually.
That's nothing unique to developer edition. You're just more likely to see something that'll trickle down to release builds soon anyway.
Personally I've managed to live with some annoyances on nightly for a few weeks until they got fixed.
