Found this post on Reddit by user ajorpheus and thought it would be worth sharing:
You might be interested in knowing that there is now an unofficial up-to-date palemoon build (26.0.0) for OSX: https://forum.palemoon.org/viewtopic.php?f=41&t=10847&sid=8884ca5df7cb55adb954d304466f8e01
Also, efforts are underway to document the process of building OSX: https://forum.palemoon.org/viewtopic.php?f=41&t=10389
Pale moon is a fork of Firefox that some people prefer because it seems to be faster, and it doesn’t force the new look on users. Many (but not all) Firefox addons can be used with it. Official builds are only created for Windows and Linux, and OS X users are usually left out in the cold.
Here’s a better description from the Pale Moon web site:
Pale Moon offers you a browsing experience in a browser completely built from its own, independently developed source that has been forked off from Firefox/Mozilla code, with carefully selected features and optimizations to improve the browser’s speed*, resource use, stability and user experience, while offering full customization and a growing collection of extensions and themes to make the browser truly your own.
There is no link to this unofficial build for OS X on the official Pale Moon site (other than in their user forum) but nonetheless it seems to work pretty well, in fact I’m using it right now to compose this post. I make no guarantees, but if you are feeling a bit adventurous, give it a try – you just may prefer it to the increasingly lethargic Firefox!