Very nice idea! Rated 4 out of 5 stars
But it needs some enhancements.Currently it doesn't appear on links and pictures (that is right), but still appears on regular text, so it is impossible to lightening it, copy etc. It is impossible either to use context menu by right clicking (it locks this addon, and only then I can use right click).It would be better if this square will appear 20-30 pixels above the cursor and with some delay (1-2 seconds) so, that if the user will want to hit it - he will move the cursor to this square (that will prevent it to move 20-30 pixels above cursor), i.e. the square will be in 20-30 pixels from cursor only if cursor doesn't hit the square.The square itself might have lower opacity and get 100% opacity only on hitting it.