Bug 858291 Flicks promo looks broken at lower resolutions

The Firefox flicks promo thumb on the home page was being incorrectly positioned when changing viewport breakpoints. 

To reproduce, re-size the browser when the flicks tab is not visible, then switch to it after re-size. The bug occurs due to jQuery reporting a width of `100` for an element when it is hidden, resulting in an incorrect left offset.

Fixed by setting default `linkWidth` values for the different screen sizes.