Comment 13 for bug 1830096

(In reply to Dave Townsend [:mossop] (he/him) from comment #6)

> If the builds for each release are from the same source then I don't think it would be an issue for the Firefox build ID to match across those builds, though I also imagine that sharing profiles between different Ubuntu releases is going to be rare.

Indeed this wouldn't be an issue, rather a logical thing: two binary packages of the same version of firefox (sharing a single source package) have the same build ID.

> The chief thing that we care about is that if the Firefox code is newer then it should have a larger compatibility version than previously. The compatibility version is defined as `<version>_<appbuildid>/<platformbuildid>` (the latter two are the same in Mozilla builds). We compare as if the string is a valid toolkit version (https://developer.mozilla.org/en-US/docs/Mozilla/Toolkit_version_format), and to make that the case we do some special parsing in the case where the buildid is the expected number of characters that are generated from Mozilla builds, otherwise we just use the literal compatibility version for comparison.
>
> I am not sure about other uses of the build ID in Firefox, but I think one viable option is just to set the build ID to your "build2". This would lead to a compatibility version like `67.0_build2/build2`.
>
> […]
>
> What do you think of that?

This makes sense to me, and sounds like it would work. Note that "build2" in that context comes from the upstream build candidate, it's not an Ubuntu-specific thing: https://ftp.mozilla.org/pub/firefox/candidates/67.0-candidates/.