...still waiting for the ephemeral "Link To This Post" button to reappear...

I'm still getting just a dark grey square (Firefox 33.0.2, all plugins and addons disabled)

This might have something to do with Flash. Copying to a clipboard is actually extremely complicated and most libraries that handle this use some sort of flash/javascript mixins. I'd make sure flash is installed through your browser. Note: The flash plugin must be installed on the browser in use. 
http://get.adobe.com/flashplayer/

On a side note: AdBlocker will block .swf files if set to do so and sadly a .swf actually replaces the button behind the scenes. You can see this if you right click the button, it will actually give you an Adobe Flash Player menu instead of basic browser menu like the buttons beside it.

Why are you using flash to do this? I'm probably not the only person who browses with all plug-ins (including Flash) disabled... ...or maybe I am !?!?

A simple link in each post that link's to that post is simple HTML (e.g. the number at the top right corner of the post here http://www.daz3d.com/forums/viewthread/40538/P30/#709239 or http://forum.runtimedna.com/showthread.php?94377-November-2014-Theme-Vote&p=856787&viewfull=1#post856787 - yeah, they probably use PHP or some such to create the link; but I get served plain HTML).

The user just clicks on the post number and then cuts-and-pastes the URL from the browser's address bar.

Using flash purely to put the URL into the clipboard seems akin to using a sledgehammer to crack a nutshell.

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The 3Dcheapskate* occasionally posts sensible stuff. Usually by accident. And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU or something else.
*soon only to be available in two flavours -  DAZ and Renderosity