“Mom, what were you like in the 90s?” The question has gone viral—and the response, a flood of celebrity flashback montages, captures the likes of Halle Berry and Courteney Cox in their Kodachrome heyday, set to (what else?) the Goo Goo Dolls’ “Iris.” The trend dovetails FX’s Love Story, the trashy yet wildly popular mini-series purporting to depict the behind-the-scenes courtship and ill-fated marriage of Carolyn Bessette and John F. Kennedy Jr…