By default, the Firefox new tab page has ads and sponsored content, which neither Chrome nor Safari have. This "feature" certainly decreases trust in Firefox as the more privacy-friendly option, although it's easy to disable for experienced users.
Targeted advertisements like the ones built into Firefox's new tab page are the exact kind of thing that privacy-conscious people like to block. When I recommend Firefox to a less-technical friend or relative and suggest that they use uBlock Origin or another powerful ad and tracking blocker, it's awfully ironic that the default new tab page is full of targeted advertisements. It's purely perception, of course, but it's the kind of thing that almost certainly isn't helping Firefox compete against Chrome.
