about: config hack on Firefox
In fact, you can use Firefox:
- Go to the "about: config" section
- Find "layout.css.devPixelsPerPx
- Change it to the desired ratio (1 for normal, 2 for retina, etc. -1 by default.)
Screenshot:

Refresh your page - boom, your media query is now kicked! Hats for Firefox for being awesome for web development! Heads up, not only will the website size be doubled now, the Firefox user interface will also be doubled. This doubling or scaling is necessary, as this is the only way to examine all the pixels on the standard pixel screen.
This works fine on Windows 7 with Firefox 21.0, and also on Mac OS X with Firefox 27.0.1.
If you do not use multimedia queries and other more complex logic (i.e. you write to all HiDPI images), you can simply increase the scale of your browser up to 200%. Chrome emulation is a useful tool, as well as pings in media queries, but since it prevents scaling, you cannot check the image quality.
Scaling on Firefox and Edge
On Firefox and Edge, if you zoom in, dppx-based media queries are currently running. Therefore, this simple approach may be sufficient, but keep in mind that the functionality is reported as a “do not fix” bug for Firefox, so this may change.
andrewb Jun 21 '13 at 5:17 2013-06-21 05:17
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