I think it would be a mistake to completely remove the developer tools from the non-developer version of Firefox, but I'd also be fine using a different developer-centric browser for the majority of my development understanding that there may be small differences and edge cases that need to be tested on numerous other browsers.
One of the PM did a comment and gave as an example that they will block self-xss on Firefox, which won't be blocked on the developer version. It won't affect much but you can already see how it's affected. You will be able to run something on a browser but won't be able to do the same on another.
I seriously don't see why we need a developer version of a browser, except removing developer stuff from the real browser and/or adding different support (which will give you issue when you will move to a real browser).
I don't really agree with this part; it's going to be using the same rendering and JavaScript engine so I wouldn't expect the experience to be different at all it'll just have far better access to developer tools.
Having said that, Mozilla didn't exactly put much of any content into their blog post so I could end up being wrong.
In the vast majority of scenarios we don't think about using the same processor to experience the same thing a user does. (Certainly driver developers and other low level h/w people will occasionally run into h/w bugs but they're in a very niche field).
For instance, when I want to debug my website I go to the dev tools within the browser I'm viewing because I know that my users are viewing the same browser (typically). Having an entirely different developer browsers makes the debugging experience less realistic. It puts you in a position where you don't truly experience what the user does but what you feel more comfortable experiencing.