This is how much Netvibes would consume just to access it (from about:cache):

Memory cache device

Number of entries:	275
Maximum storage size:	32768 KiB
Storage in use:	174243 KiB
Inactive storage:	0 KiB

It takes approximately 170 MiB of memory cache whenever I access my Netvibes, and the maximum limitation don’t even apply; I guess I’d put too much widgets on the page…