You can't compare that. Chrome, Firefox, IE, Opera, etc all try to do the same stuff, they have the same goal and want to do the same. A developer version of a browser won't have that goal, it's goal is to do something else... it will do it differently.
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).
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).