Standardising firefox plugin installation

[Christopher Aillon]

David Nielsen wrote:
> It's come to my attention through painful experience that if you install
> a plugin like gnash or the totem plugin there doesn't seem to be a set
> standard for where to install these. This leads to many issues like
> other gecko based browsers, like my beloved Epiphany, doesn't pick these
> up.
> 

It's been $libdir/mozilla/plugins since the Red Hat Linux days.  If you 
feel the need to go through some formal process of review for its 
location, go for it, but too many things already rely on that directory 
and it won't be changing.