What did I do? "Mouse Klutz"

Good day all. Working on a score and tapped a combo of keys to get a very interesting effect. I have no idea what combo, but I'd like to repeat it.
Basically what happens is : when I drag the score to the left to see the measures on the right side of the page ( fine placement of notes ) , the Key Signature / Time Signature and Clefs become blue and stay with the left most side of the staff. Similar to locking a set of cells in a spreadsheet app so that you can always see the first line legend.
Cool effect, might come in handy, but haven't a clue how I did it.
Thanks. Really Thanks - such a great tool!
Al