User Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) snap Chromium/72.0.3626.121 Chrome/72.0.3626.121 Safari/537.36

Steps to reproduce:

This is a request to make the firefox snap build against the core18 base snap.
I am going to look into and test the changes needed in snapcraft.yaml.in to make that happen.
This will require the build environment to be upgraded to Ubuntu 18.04.

Thank you very much for filing this bug, Olivier.

Ken VanDine (from Canonical too) reached out to me a few days ago and gave me some context about this request.

It would allow to use newer glib/gtk, and would make themes would work. Per Ken, right now that's the only snap that doesn't honor themes properly.

The Firefox Snap is currently made by 2 phases:

• First, we make the regular Firefox x86_64 build. This one is built on Debian[1].
• Then we extract this build, add some extra files and repackage the whole thing into a snap.

My understanding of what's currently needed is: we need to support a new Linux distro. I don't know what's the effort to achieve this. Mike, does this fall under the Build team? If so, how big would the effort be? If not, feel free to redirect :)

[1] For instance:

• https://treeherder.mozilla.org/#/jobs?repo=mozilla-beta&revision=13bfcad39c39edcd4e3fc5b26fd62b25d338235f&selectedJob=232378448 uses this docker image https://tools.taskcluster.net/groups/HESEhSiCTp60wGqdbq8XPQ/tasks/NmNQ_Ns7QH-h8-01-OImbQ/details
  [2] https://searchfox.org/mozilla-central/rev/8ff2cd0a27e3764d9540abdc5a66b2fb1e4e9644/taskcluster/docker/firefox-snap/runme.sh

I'm not sure what would be involved here, particularly with regard to using a new glib/gtk. glandium, your thoughts?

We shouldn't need to change anything for the Firefox build. If we need to, that means there's some bug that should be fixed.
From there, the snap thing is free to use whatever it wants.

That's not a bug in firefox itself. The requirement for building against a newer version of GTK stems from the gtk-common-themes snap, which enables apps installed by third-party snaps to be themed according to the user's desktop settings.

The firefox snap currently cannot connect to the interfaces provided by gtk-common-themes, because of ABI incompatibilities: gtk-common-themes supports only GTK ≥ 3.20, whereas the current build of firefox that is packaged as a snap is built against GTK 3.18.9.

Rebasing on core18 would require building the assets that go into the firefox snap on Ubuntu 18.04.

Firefox is not rebuilt for snaps, as per comment 1. It is built against GTK 3.4. If running that build against GTK 3.20 doesn't work, there's a bug in Firefox. If the problem is that the snap contains GTK 3.18, and that Firefox uses that, and it should use GTK 3.20 instead, then sure, it should be a no-brainer to update the base image for the snap.