DeIdol is an extension for Firefox (currently) that replaces the banner image on the PC Master Race subreddit with a modified, more community-centered banner image created by /u/mastermx.
The extension runs a simple page detection that, once on the PCMR subreddit, will execute a script that injects the following rules into the page:
background: url('pcmr-banner.png') no-repeat scroll 0% 0% #000 !important;
background-size: cover !important;
This is the first Firefox extension that I have ever tried to make. If it is rubbish, non-functional or otherwise lame then there's your reason. I'm truly sorry.