Harper FF extension breaks WP post editor scroll bar

When editing posts in WP 7.1 (also 7.0.4 when I test it with other sites) post editor using FireFox 155.0 with Harper V2.0.8 extension, the scrollbar shoots to the bottom every time I touch any part of it, even the little arrows at the top or bottom. This is pretty much the only place I want to use Harper, but it makes the editor pretty much unusable. Using Windows 11.

I've tried a staging site with all WP plugins turned off, but it still happens. I don't see anyone else reporting this issue — can you reproduce it, or is it just me? It's definitely Harper, because the bug disappears when I switch it off in the add-on manager. I haven't seen this behavior anywhere but the WP post editor so far.

Start by reproducing the issue in the WordPress post editor with Harper V2.0.8 enabled, using Firefox 155.0 on Windows 11, then compare behavior with Harper disabled. Trace the extension's interaction with the editor and scrollbar; done means the scrollbar remains usable in the post editor while Harper is enabled.

Written by the indexing model from the issue text.