I would guess you have an old graphics card with out-of-date/broken drivers, and different browsers have different checks to revert to slow software rendering if the graphics drivers are broken. So all you're seeing is the difference between hardware rendering and software rendering depending on whether the browser accepts the drivers. Even if it's fast there may be crashes or glitches due to broken drivers.
Most modern hardware should be fine, this kind of thing only tends to affect old devices.