The function allocation code (js_NewFunction in jsfun.c) in Firefox 1.5 allows attackers to cause a denial of service (memory corruption) and possibly execute arbitrary code via user-defined methods that trigger garbage collection in a way that operates on freed objects.
Exploitability
AV:NAC:LAu:NImpact
C:PI:PA:P7.5/AV:N/AC:L/Au:N/C:P/I:P/A:P