Synonyms for Unfirm (same or very similar meaning)
WordNet sense 1 (not firmly or solidly positioned):
unsteadyWordNet sense 2 (not firmly placed or set or fastened):
unfixedWordNet sense 3 ((of soil) unstable):
shiftingWordNet sense 4 (not compact or dense in structure or arrangement):
looseFrom the ODE community, based on WordNetadd/edit