Element hiding debug functionality causes hang in older Firefox

Environment

ABP 3.8.4.2581
Firefox 51.0 / Windows 10 (1903)
Firefox 52.0 / Windows 10 (1903)

Working as expected in Chrome browsers. Working as expected in Firefox 76.0.1 (latest).

How to reproduce

1. Open [ABP Icon] > [Options].
2. Enable the debug preference via the console.
3. Navigate to hide-if-contains test page.
4. Add the first filter to ABP.
5. Refresh the test page.

Observed behavior

Firefox completely hangs/freezes and needs to be killed/reopened.

Expected behavior

ABP functionality to not hang Firefox.