Web UI build for 9.10 goes through without error but it produces a jar which does not contain web ui source code.
As a matter of fact, the ftest job is red:
It only deploys index.jsp without any other resources (except i18n ones)
It started on March 27th 2019 revealed by https://qa2.nuxeo.org/jenkins/job/9.10/job/plugins_nuxeo-web-ui-2.2_9.10/2236/
While backporting vaadin date-picker for 9.10
ELEMENTS-791, we did not freeze this bower dependency and they released v.3.3.3 and this commit introduced a change to rely on ../../polymer/lib/mixins/disable-upgrade-mixin.html which we don't have in our frozen other dependencies.
9.10 >= HF28 breaks on FF < 63 because of that.