Two-finger swipe gestures stopped working in search page

[szdarkhack]

Description
The (Windows) two-finger scroll touchpad gestures (scroll left/right, which, on Firefox at least, translates to page back/forward when reaching the edges of the page) have stopped working in recent versions. According to some quick testing this appears to have happened between versions 24.6.24.0 and 24.7.1.0 (the former works fine, the latter doesn't).

Steps to reproduce:

1. Enable 2-finger scrolling (Windows settings -> Bluetooth & devices -> Touchpad)
2. Open the Yomitan search page in Firefox (Alt+Ins or via menu)
3. Perform a search
4. Attempt to go back to the previous page by swiping with two fingers.

Browser version
Firefox 128.0

Yomitan version
24.7.1.0 or later

Exported settings
yomitan-settings-2024-07-22-18-43-24.json

[szdarkhack]

I've narrowed this down to the overscroll change introduced in #1155. While that change definitely makes sense for the popup, it creates this unintended issue with the search page (and doesn't seem to offer any benefit in that case). Would it be possible to set overscroll-behavior to contain only on the popups? There is also the alternative of only setting the overscroll-behavior-y, but I think the 1st option would be the best of both worlds.