Sluggish scrolling on a non-high-end (mobile) device

**Describe the bug**

Scrolling any of the timelines as well as the settings screen has a noticeable lag on a less powerful device (see below); I suspect some CSS filters (blur?) might be at fault, but not sure how to confirm this. If this is so, maybe a toggle somewhere in settings for disabling expensive eye-candy would help?

- Which site: both dev.phanpy.social and phanpy.social
- Which instance: _any instance_

**To Reproduce**
Steps to reproduce the behavior:
1. Go to the home timeline or settings (as an example)
2. Try scrolling the page;
3. Notice annoying lag.

**Expected behavior**
The page should scroll / operate without any heavy-lifting on the CPU or GPU or power drain.

**Screenshots**

https://github.com/cheeaun/phanpy/assets/479389/eaaf04dd-bb7c-4fcc-b0bd-0b4c0f510877

**Smartphone (please complete the following information):**
- Device: Sony Xperia 10
- OS: LineageOS 20 (Android 13)
- Browser Fennec F-Droid (Firefox)
- Version 120.0.0

Reproduce the lag in the home timeline and settings screen on the reported Xperia 10 with Fennec Firefox, then profile scrolling to identify whether CSS filters or another frontend cost is responsible. Done means scrolling is responsive on less powerful devices without excessive CPU, GPU, or power use, with any performance setting or scope clearly established.

Written by the indexing model from the issue text.