Thank you for your feedback!
Regarding the horizontal scrolling, the extension does not currently support a horizontal scrollbar because most search expressions fit within the window's width. However, I will consider ways to improve this (larger window or horizontal scrollbar).
[EDIT] Horizontal scrollbar added in version 1.74.
As for the search window not closing when clicking on the webpage, this feature was added recently due to user requests for a persistent window. You can revert to the previous behavior by disabling the "persistent search window" option in the display settings (click the cogwheel).