What are some possible side effects (if any) experienced in adults because of having many febrile seizures as a small child?

See below: This is a tough one. If they were short febrile seizures, brought down by meds/cooling etc, then probably none. If they were longer and sustained then there is a possibility of lingering side effects, but from here it is difficult to say. Talk to your local md and discuss, if needed go further and talk to a neurologist.

Definition issue: Febrile seizures are innocent problems of an immature nervous system that kids grow out of & don't produce learning disabilities or other issues in adulthood. The problem comes with the overlap with a true seizure disorder of early childhood. Infants or children that go on to have epilepsy in their teens or adulthood can also have seizures during fever.Once you go > 3 fs i worry about epilepsy.

Depends: Most febrile seizures are benign with no side effects in adulthood. However, if febrile seizures are very prolonged, they may lead to epilepsy in adulthood.