Do not jest..
You would be surprised to know in much scripture and for prophecy, there exists deliberately, at least dual purposes and meanings embedded in them. This may include two or more 'before the foundation of the world' expressions or 'before the world was or began' for this subject. I prefer the 'foundation' expression as it gives more meaning, the idea of the beginning of something about to be created in the world.
Two types:
1. 'before the foundation of the world' meaning actually right before the 1st Adam, the first man was created, and not the earth or universe, and 2., In what
@Waiting on him was referring to, 'before the foundation of the world' meaning the current local known world of people existing right before Christ. This particular world that he who live in and pronounce the Kingdom of God is at hand.
And Christ reiterated this promise of the Father he knew of with eagerness in prayer, in the Garden.
The idiom then: Of the glory I had with you (meaning, the glory of immortality you promised me) before the foundation of the world (meaning, in your plan, both before the 1st Adam was created and also before Christ the 2nd Adam was in this world of national Jews who would see his glory in person - of immortality).
All this was in the mind and plan of God, before the 1st and 2nd Adams. And his Son read it well -he had close contact with his mind all the way.
Just curious what do you think of,'...
O Father, glorify thou me with thine own self...', the part you did not address?
Thanks.