How to work with documents directly in developer mode?

Sorry for my English, google translator is to blame for everything.

I need your help.

I am working in Firefox Developer Edition (html / css) browser.

I edit the styles in the browser and save my work.
When I try to save styles, I am prompted to choose which directory to save the document to. Not very convenient, I would like to automatically save and replace the document I was working on. How it is implemented in editors (save or save as).

Is there such a possibility in the browser:

  1. Directly work with html documents?
  2. Directly work with css documents?