1991 to 1997 Mercury Cougars and 91 to 96 Ford Thunderbirds run a high/low beam combination 9007 headlight bulb.
If still own one of the last big cats or thunderchickens, then you will have this happen when you replace the headlights. This plastic headlight retainer nut should have three ramps and three tabs, but it's down to only one tab.
My other retainer had no tabs left.
At this time you won't find a replacement listed for a Ford product anywhere, but Dorman 42420 is listed as 9007/9004 retainer for GM products.
Throw the one for the 9004 in the trash and look at the 9007 version. It's just slightly shorter than the stocker, but everything that matters is in the right spot.
Fits perfectly and works great.