Unless you audit the source of every piece of software you use as well as that of every compiler used in making their binaries, you aren't in a position to make that sort of absolute statement. OSS has benefits but for most users they are delegating the code review to someone else, which makes it very similar to proprietary code.
There is an argument to be made about motives with free vs non-free software, but open vs closed source is for most people much less important.
Transparency in software releases isn't all-or-nothing. The parent comment makes a good point about preferring more transparency (free and open source software) over less transparency (proprietary software) as a consumer.
However, the parent comment is a bit misplaced since Ghostery appears to be released under the Mozilla Public License 2.0.
There is an argument to be made about motives with free vs non-free software, but open vs closed source is for most people much less important.