In 16.04 the package suggests vital, but non-existent packages chromedriver and firefoxdriver

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It took a look at this and it might be two separate issues for each of the drivers.

The firefox driver seems to have only been packaged recently (see https://launchpad.net/ubuntu/+source/selenium-firefoxdriver or the publishing history) and is only available in 16.10 and newer. It should be possible to request a backport of this to 16.04, see https://help.ubuntu.com/community/UbuntuBackports for details on this.

Chromdriver seems to be another story. In Debian, it is built as a transitional package for chromium-driver,
 but in Ubuntu the package only offers chromium-chromedriver. Compare the list of binaries on https://tracker.debian.org/pkg/chromium-browser with the ones listed on https://launchpad.net/ubuntu/+source/chromium-browser. This might be another small difference since chromium is packaged directly in Ubuntu separate from Debian, but I don't know if there is a reason for the driver package names to differ. I've taken the liberty to mark this issue as also affecting chromium-browser for this part.

Where do you see that chromium-browser suggests chromedriver and firefoxdriver in xenial?

$ apt show chromium-browser
Package: chromium-browser
Version: 58.0.3029.81-0ubuntu0.16.04.1277
[…]
Recommends: chromium-browser-l10n
Suggests: webaccounts-chromium-extension, unity-chromium-extension, adobe-flashplugin
[…]

> Where do you see that chromium-browser suggests chromedriver and firefoxdriver in xenial?

Sorry for the confusion, python-selenium suggests/recommends them (http://packages.ubuntu.com/zesty/python-selenium). Firefoxdriver has been added in newer releases, but the chromedriver package is still missing.

The reason I marked chromium-browser is that the package seems to be missing due to a delta between Ubuntu and Debian.

In Debian the chromedriver package exists and is a transitional package for chromium-driver. Both of these binary packages are part of chromium-browser (https://tracker.debian.org/pkg/chromium-browser). However, chromium-browser in Ubuntu has a package with at third name; chromium-chromedriver (https://launchpad.net/ubuntu/+source/chromium-browser).

I am not sure why the *driver package names differ, and I haven't found any specific notes on this. In order for python-selenium to find it, I reckon either python-selenium needs to be patched with the Ubuntu package name or chromium-browser needs to provide a (transitional?) package named chromedriver.

That makes sense.

This is ongoing to be fixed in disco, feel free to convert in an SRU.

and looks really similar to 1685037