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?

Yes to both. Use Chromium. I’m not sure about Firefox, but Chromium has that feature. Just reload Firefox between edits.