What you have is moisture in the headlamp unit, which is normally airborne (and invisible) in warmer weather. 2 ways to tackle this depending on whether moisture is 'trapped' in a sealed unit following a bulb change, or if the sealed has been breached, allowing water in.
Mark I Focuses had this problem, the cause of which was determined by running the light on main beam with the lens covered by black paper and the sidelight bulb removed. This would cause the unit & air within it to heat up, dispelling the moisture, then after around 10 mins with the light on, switch off and carefully
replace the sidelight bulb as soon as possible. If unit was sealing properly - moisture will not return, if moisture returns, the lens is not seated properly, and its up to you whether to repair or replace.
The above is a simple enough & cheap test, which will either repair the problem, or point you in the right direction.
I've seen this work on my Scorpio.