Before anything make sure you have installed Violentmonkey* for Firefox or Tampermonkey for Chrome, Opera, Safari or Edge
Because derpibooru has a draconian CSP headers, firefox users are also going to need Laboratory by Mozilla
Install the addon and set it to use the following custom CSP for derpibooru:
default-src 'self' https://derpicdn.net; font-src 'self' https://derpicdn.net; img-src 'self' data: https://camo.derpicdn.net https://derpicdn.net; script-src 'self' 'unsafe-inline' https://derpicdn.net; style-src 'self' 'unsafe-inline' self https://derpicdn.net
One final reminder:
* Once configured, firefox users can remove the addon buttons from their toolbars and proceed to ignore its existance
After that simply click the download link to be prompted to install the script.
*Important Note: Do NOT use Greasemonkey. It's dead, and the script may not work with it.