MacOS notarization
With the introduction of macOS 10.15 “Catalina” Apple introduced new notarization requirements that all software must be signed and notarized centrally.
Whilst the geckodriver binary is technically both signed and notarized, the actual validation can only be performed by MacOS if the machine that starts the geckodriver binary for the very first time is online. Offline validation would require shipping geckodriver as a DMG/PKG. You can track the relevant progress in bug 1783943.
Note: geckodriver releases between 0.26.0 and 0.31.0 don’t have the notarization applied and always require the manual steps below to bypass the notarization requirement of the binary during the very first start.
Offline mode
There are some mitigating circumstances:
Verification problems only occur when other notarized programs, such as a web browser, downloads the software from the internet.
Arbitrary software downloaded through other means, such as curl(1) is not affected by this change.
In other words, if your method for fetching geckodriver on macOS is through the GitHub web UI using a web browser, the program will not be able to run unless you manually disable the quarantine check (explained below). If downloading geckodriver via other means than a macOS notarized program, you should not be affected.
To bypass the notarization requirement on macOS if you have downloaded the geckodriver .tar.gz via a web browser, you can run the following command in a terminal:
A problem with notarization will manifest itself through a security dialogue appearing, explaining that the source of the program is not trusted.