My experience in a chromium-based browser was multiline text selection was not good.

Any time you drag over space between lines, it selects something else.

I think that's just the standard behavior of the selection algorithm with that particular layout. FF might be applying some kind of debouncing or hysteresis to keep it from flickering, but if so it's making all selection sluggish.

Yes, unfortunately SVG does not support line breaks or wrapping, so much like pdf text selection is on a best effort basis

FF142 macOS had no issues with text selection on my end.

Yet another example of how maddening it still is when designing websites that have the same experience regardless of how it is viewed.