Prevent Find (Ctrl+F) resizing letterbox on other tabs

Steps to reproduce:

1. At the default window size, open two tabs.
2. In one tab, open a domain/website.
3. In the other tab, physically type a different, unrelated domain/website, and open it. Physically type it so that the two tabs are as identifiably separate as they can be in one session. No referers or variables passed in click-through URLs.
4. Notice that each page's area fills the default window size to its edges as they are supposed to.
5. In the first tab, open the browser's Find box (Ctrl+F) as if you were searching for text on that page. Notice the vertical size of its letterboxed page area shrink as it's supposed to.
6. Click on the second tab to view the different, unrelated domain. Notice its tab does NOT have a Find box at the bottom, but its letterboxed page area shrunk nonetheless.
7. On the first tab, close the Find box. Notice the page area grow to its original size.
8. Click on the second tab that never had a Find box. Notice its page area has also grown to its original size.

Thus, opening Find on one tab passes the indication of its opened state to all tabs.

Expected result: Opening Find in one tab would not affect the letterboxes of other tabs.