What a load of FUD. I've found the Pale Moon people, on IRC and otherwise, to be extremely helpful. I use Pale Moon on linux exclusively and it is well supported.
As for being "frozen" in the past, have you used Pale Moon recently? Just because the version number doesn't increase at the rate of Chrome or Firefox doesn't mean they aren't making improvements from sub version to sub version. It's noticeable.
And what do you mean by "all the HTML 5 features"? Do you mean they refuse to implement the digital rights management extensions that were forced into Firefox? All the better. The Pale Moon team is consistently on the side of the user.
Firefox has added DRM, removed about:config options, added unremoveable bloatware (ie, Pocket), and they intend to abandon the vast majority of the existing XUL based add-on/extension ecosystem.
Pale Moon's future is as bright as Mozilla Firefox's is dark.