In Safari the button contains bits of the "delete" text, which does not appear in Mozillla. See the screenshot.
Nominated as an LTS candidate, because it impacts UI.
The fix will have 2 weeks of soaking by the RC cut-off
Code changed in jenkins
User: Manuel Recena
JENKINS-35178 Fix close button in Safari (#2378)
(cherry picked from commit d35c7de73b1b78e1aa47470bdff36b0f60884c8d)