Selecting a line in CI job trace using triple-click selects the previous line also

Summary

Started seeing this after collapsible job traces MR hit dev. When I select a line using triple-mouse-click, the line immediately before the intended one also gets selected. Even though the selection is not visible, it gets copied when attempted to copy using Ctrl-C. See gif below for a demo.

collaps

I am using Firefox 67, on Debian.

(Summarize the bug encountered concisely)

Steps to reproduce

  1. Go to a build job in dev - for example https://dev.gitlab.org/gitlab/omnibus-gitlab/-/jobs/4648327
  2. Triple click on any line - see it gets selected.
  3. Press Ctrl-C to copy the selection
  4. Paste it somewhere
  5. See that the paste brought in two lines - the one we selected and the one immediately before it.

/cc @filipa