Lemme test it
Then maybe... just mayyybe... I'll upload it onto a better host for you, so it won't die XD
If you want, that is...
Edit:
Okay, here are my thoughts...
Will the mouse be able to be used on the menu?
Since you said it uses the mouse, I assumed that it'd also be able to access the menu, but then after clicking like 5 times, I realized it couldn't XD
Maybe you could make a way to move/remove an already placed tile?
And also with the Exporting filename input, maybe make the Backspace key actually do something XD
How big can the tileset get anyway?
It's a good job though...
*moves*