Most of the time, missing extensions are caused by old graphics drivers. Make sure you have the latest graphics driver, either from your OEM or directly from NVIDIA/Intel/AMD. Usually, your OEM will have outdated drivers, so try and find drivers directly from e.g. NVIDIA or Intel.
Some of the older low-end integrated cards (especially the GMA945 - ugh!) are hard to provide compatibility for; I don't know if it'd be worth supporting those. However, Intel's newer cards like the Intel HD4000 are actually quite decent, so it should really only be an issue with more or less ancient cards.