The only way to do it without any problems is, unfortunately, to test it and
see which combinations work best. I believe to recall installing grip from
the Ubuntu repos, together with some libraries which it needed which were
only in Ubuntus repos. All went well and I had grip running without problems.
I'm quite sure though there was some non-free software installed that way, or
at least some stuff that is patent-encumbered and avoided by the Trisquel
team for safety reasons. I don't have grip installed anymore.
I've been using global-menu and icecat PPAs for some time without problems
too.
At some point global-menu broke (I believe due to updated gnome-panel) and
Abrowser became much more recent, so I needed no icecat and disabled the PPA.
