Another approach could be something that sort of resembles B.
When the find UI opens, it has the same effect as displacing the page, the way full-width find bars do. The difference would be that the UI stays as it is and isn't changed into a full-width find bar. The null space to the left and right of the find bar would still allow whatever it's overlaying to shine through.
The only move to make now is figuring out what happens when the user isn't sufficiently scrolled down far enough, i.e., the null space around the find UI when the user is scrolled to the very top of the page is actually void space. What do you put there? I suggest silently[1] extend the scrollable area of the page by adding a quasi-content area. It's quasi-content because it's not actually part of the page--it's just part of the scrollable area. It pulls its color/background pattern from the page's background style.
Another approach would just be to have the find UI extend into the browser chrome, temporarily shrinking the location bar.
[1] being careful here not to set off any events or changing the way, e.g., event coordinates look to script on the page
When the find UI opens, it has the same effect as displacing the page, the way full-width find bars do. The difference would be that the UI stays as it is and isn't changed into a full-width find bar. The null space to the left and right of the find bar would still allow whatever it's overlaying to shine through.
The only move to make now is figuring out what happens when the user isn't sufficiently scrolled down far enough, i.e., the null space around the find UI when the user is scrolled to the very top of the page is actually void space. What do you put there? I suggest silently[1] extend the scrollable area of the page by adding a quasi-content area. It's quasi-content because it's not actually part of the page--it's just part of the scrollable area. It pulls its color/background pattern from the page's background style.
Another approach would just be to have the find UI extend into the browser chrome, temporarily shrinking the location bar.
[1] being careful here not to set off any events or changing the way, e.g., event coordinates look to script on the page