unfortunately, it won't work on Pale Moon due to an issue with Firefox's addon SDK relying on a hard coded name of some sort (I'm giving a vague answer because I can't remember the exact details)...
While RES isn't officially supported on nightly builds, I am told it will work on Firefox's nightly x64 builds.
It's worth noting, however, that most people don't really need a 64-bit browser. The main advantage is being able to access way more memory - but you can already use over 2gb of memory with 32bit firefox. If you browse with metric loads of tabs open, you might use 2gb - but if not, you're not even pushing the 32bit memory limit, so you're probably not really benefiting from a 64bit browser anyhow. Food for thought :-)
P.S. Don't blame RES because Reddit redesigned the entire site. If you want all your old goodies back, click preferences, scroll all the way down to the bottom, and next to "Beta Options" uncheck "Use the redesign". Now you're back to the old site and everything works again.
If it weren't for RES, I wouldn't have been able to maintain my unhealthy reddit addiction because of the off-putting default interface. I've been a huge fan of this extension for years, to the point where the regular site is unusable now. Absolutely essential for anyone who spends any amount of time on reddit.
I used to really love this, especially the in-line photo viewer. But after reddit redesigned their website, the main function I use this for, the photo viewer, no longer works. Guess I'm uninstalling. It used to be super good though.
we would appreciate if you'd post to /r/RESIssues where we provide (free) technical support to users having issues, instead of leaving us a 1 star review without even giving us the opportunity to help...