[greyhat]

The slowness in Firefox appears to be solely due to this:

  @media (min-width: 1180px) {
    body:not(.no-literate) .content-root {
      background-color: #fdfcfc;
      -webkit-box-shadow: inset 780px 0 #fff, inset 781px 0 #e7e7e7, inset 790px 0 3px -10px rgba(0,0,0,0.05);
      box-shadow: inset 780px 0 #fff, inset 781px 0 #e7e7e7, inset 790px 0 3px -10px rgba(0,0,0,0.05);
    }
  }

Removing it in the Firefox style editor restores normal performance.

Edit: And they have commented out the box-shadow! Hah.

[KaoruAoiShiho]

I've been dealing with this lag in firefox for the past 6 or 7 years. It's hilarious to me that they still haven't fixed it. Just one of the reasons I've been extremely negative on firefox.

[greyhat]

This is the first time I've seen something like this. I use Firefox full time for development and personal use and do a lot of front-end work. ¯\_(ツ)_/¯

[agumonkey]

Not a great solution but I got a bookmarklet that removed any fancy css rule (shadow, alpha, ...).