Let's suppose that, hypothetically, you were playing an online browser-based version of Minesweeper in which there was no capacity to flag a square as a mine. Is there a bookmarklet that would more or less let you do this? (That is, make a small mark somewhere on the screen that you could easily later remove, for the purpose of keeping track of spatial information.)
I haven't been able to come up with any good search terms for finding something like this. The closest thing I can find is a text highlighter.
