Firefox caches might refer to garbage collected builds.

[nbp]

Describe the bug
Firefox (firefox-bin) relies on build-id to invalidate some of its internal caches. These caches might have content which is referencing absolute path of previous installs of Firefox.

When updating firefox dependencies without a firefox update, the build-id (timestamp of the build) would be identical. Thus none of the caches would be invalidated, and these caches would still reference the absolute path of the previous installation. This can cause issues where embedded addons are no longer found after a garbage collection.

The binary derivation for firefox should change the gToolkitBuildID strings to make it different between builds which have different dependencies.

One hackish idea would be to replace the last 4 digits mmss with a 4 digit number which is computed from the dependencies.

Additional context
See https://bugzilla.mozilla.org/show_bug.cgi?id=1704147

Notify maintainers
@taku0 @lovesegfault

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
- firefox-bin

[taku0]

We might able to generate gToolkitBuildID from $out. What is the restrictions of gToolkitBuildID? Only numbers? Should it be monotonic?