Firefox4 not picking up portable Plugins directory

During Firefox4Beta and Firefox3.6 I had no problems with saving plugins in to either one of the two plugin directories which travel with the portable app.
This of course being important for Flash and Shockwave use.
(Details on how to do this can be found elsewhere on these forums, that's not the purpose of this post-> carry on hunting sorry!)

I'm also aware of the about:config switch to turn OFF scanning for local plugins (plugin.scan.plid.all switched to false does this if you don't want to use local plugins).

I've got the opposite problem.

When I check about:plugins with the full file locations shown (about:config plugin.expose_full_path) it's ONLY picking up those installed on the host machine and NONE of those saved in either of the plugin directories. And yes, I have tried deleting the pluginreg file.

I've checked with a fresh install and it appears to be the full firefox4 which is the problem.
Anyone else spotted this/suggest a solution?