Selection flickers on mobile if there is some vertical space between the <span>s in the text layer

[nicolo-ribaudo]

Attach (recommended) or Link to PDF file here: https://home.barclays/content/dam/home-barclays/documents/investor-relations/ResultAnnouncements/FullYear2023Results/20240306-Barclays%20FY23%20Analyst%20Breakfast%20Sell%20Side%20Meeting.pdf

This also happens in the "Trace-based Just-in-Type ..." PDF, but it's less visible because its lines have a slight overlap (it's only visible in some specific areas of the document where there is more space).

Configuration:

• Web browser and its version: Firefox 124.4.0 (it also happens in Chrome for Android, and Safari on iOS)
• Operating system and its version: Android 14
• PDF.js version: Whatever is included in that firefox version
• Is a browser extension: no

Steps to reproduce the problem:

1. Select some text
2. Expand the selection across lines

What is the expected behavior? (add screenshot)

The selection should roughly follow my finger

What went wrong? (add screenshot)

Whenever my finger is between two lines, the selection jumps to the beginning of the page

screen-20240409-123911.mp4

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

I was using the one built-in in Firefox

---

I have a fix for WebKit iOS that doesn't seem to work in Firefox, but I'm experimenting with variations of it.