Heyo, I love Picross and I like your game! What you need to figure out how to do is to disable the dialogue box from opening up for the right clicker. Using space only lets you X one square at a time and that shiz is painful tedious. X'ing a lot of squares in a swipe, like the Squaring works, is a function that is natural and needed.
If I could suggest a neat feature, don't know if its within your scope, is to have completed sections highlight the corresponding numbers.
Love your effort though. I do about four 50x50+ puzzles a day.