Doing some playing and with FF 8 pinned I just noticed in the CustomDestinations file for FF8 there are entries that reference:
USERPROFILE%\AppData\Local\Mozilla\Firefox\Profiles\g2nf95sm.default\jumpListCache
On the test machine in regular non-private mode I had searched Google for CCleaner and found these entries in the FF8 CustomDestinations file:
C:\Program Files (x86)\Mozilla Firefox\firefox.exe..!.c.c.l.e.a.n.e.r. .d.o.w.n.l.o.a.d. .-. .G.o.o.g.l.e. .S.e.a.r.c.h.w.h.t.t.p.:././.w.w.w...g.o.o.g.l.e...c.o.m./.s.e.a.r.c.h.?.q.=.c.c.l.e.a.n.e.r.+.d.o.w.n.l.o.a.d.&.i.e.=.u.t.f.-.8.&.o.e.=.u.t.f.-.8.&.a.q.=.t.&.r.l.s.=.o.r.g...m.o.z.i.l.l.a.:.e.n.-.U.S.:.o.f.f.i.c.i.a.l.&.c.l.i.e.n.t.=.f.i.r.e.f.o.x.-.a.p.C.:.\.U.s.e.r.s.\.T.e.c.h.\.A.p.p.D.a.t.a.\.L.o.c.a.l.\.M.o.z.i.l.l.a.\.F.i.r.e.f.o.x.\.P.r.o.f.i.l.e.s.\.g.2.n.f.9.5.s.m...d.e.f.a.u.l.t.\.j.u.m.p.L.i.s.t.C.a.c.h.e.\.o.d.u.U.G.R.c.q.Q.e.5.9.D.+.L.Q.o.d.C.0.+.Q.=.=...i.c.o........ %USERPROFILE%\AppData\Local\Mozilla\Firefox\Profiles\g2nf95sm.default\jumpListCache\oduUGRcqQe59D+LQodC0+Q==.ico
C:\Program Files (x86)\Mozilla Firefox\firefox.exe....C.C.l.e.a.n.e.r. .-. .D.o.w.n.l.o.a.d.).h.t.t.p.:././.w.w.w...p.i.r.i.f.o.r.m...c.o.m./.c.c.l.e.a.n.e.r./.d.o.w.n.l.o.a.d.p.C.:.\.U.s.e.r.s.\.T.e.c.h.\.A.p.p.D.a.t.a.\.L.o.c.a.l.\.M.o.z.i.l.l.a.\.F.i.r.e.f.o.x.\.P.r.o.f.i.l.e.s.\.g.2.n.f.9.5.s.m...d.e.f.a.u.l.t.\.j.u.m.p.L.i.s.t.C.a.c.h.e.\.v.i.9.w.o.8.1.R.l.r.C.E.E.B.T.+.T.9.i.h.0.Q.=.=...i.c.o........ %USERPROFILE%\AppData\Local\Mozilla\Firefox\Profiles\g2nf95sm.default\jumpListCache\vi9wo81RlrCEEBT+T9ih0Q==.ico
g2nf95sm being the profile for user profile Tech.
The .ico files are PNG files and seem to be some sort of icon cache that FF now links with the jump lists. This just caught my eye and I haven't had a chance to really test in private browsing modes to see if the downloads or if now these .ico references are present.