Make sure about:newtab is blank
My understanding is that currently the desired behaviour is that
about:newtab pages should be blank instead of the default Firefox newtab page. While working on legacy/trac#30429 (moved) I realized that after applying most of the desktop patches
about:newtab is still the Firefox default. Setting
browser.newtabpage.enabled = false achieves the desired effect, but this pref is
true for current esr60 and I could not find a browser patch that explicitly sets
about:newtab to blank for current esr60.
In any case, we should probably set
browser.newtabpage.enabled = false for esr68.