Limited width Rated 3 out of 5 stars
Simple functioinality but the width of the grid is limited to 1024. The opacity is dark making it difficult to view the site sometimes. Otherwise it can be helpful.
EDIT: Eric's reply below is correct. I missed the opacity setting. The width setting can be typed in but, unless you save the grid, gets reset to the defaults when you click on the "edit" button. That is why I missed that.
To get a site width wider than 1024, you can type the number in the box (instead of using the slider).
I'll increase the site width slider in the next version anyways, since many sites go past 1024 these days.
To adjust the opacity of the grid overlay:
Right click > GridFox > Preferences > Opacity