Caution about Thunderbird 52 and binary extensions

R Kent James kent at
Wed Nov 16 18:06:05 UTC 2016

For a long time now, we have planned to stop supporting binary
extensions in Thunderbird 52. Binary extensions have been disabled in
Firefox for awhile now, and it has become increasingly untenable to
maintain that capability in Thunderbird.

Currently, the only known active users of binary extensions have all
been with extensions close to the core project: Lightning, ExQuilla, and
some Chat extensions. All of these groups gave been pursuing other
options, though it is not clear if the options are entirely problem free.

In mozilla core, bug 1314955 exists which intends to completely remove
the capability for binary extensions from the core code. That bug was
originally planned to land in gecko 52, but it missed the deadline and
landed instead in gecko 53 (but was backed out, presumably temporarily,
due to testing regressions). Even if it lands in mozilla-esr52, we would
still presumably have the option of backing it out in the branch of
m-esr52 that we will use to build TB 52.

Some may have the hope that we could continue to support binary
extensions in TB 52 if bug 1314955 does not land in mozilla-esr52. I
just want to point out that it is more complicated than just that bug.
In additional to maintaining the capability, binary compatibility also
relies on a commitment to maintain stability of interfaces and exported
symbols over the lifetime of the product in security updates. There was
a weak commitment to this from the Firefox maintainers in mozilla-esr45,
but there will be zero commitment to this in mozilla-esr52.

Maintaining binary compatibility in Thunderbird 52 would require a
commitment from the comm-esr52 manager (presumably to be Jörg) that we
will watch for interface and export changes in mozilla-esr52, and
prepare corrected versions of those bugs for our version branch of
mozilla-esr52 that would be safe for binary compatibility. This would
not be a trivial commitment, and I would recommend against that.

We have not yet landed any changes to comm-central that specifically
disable binary extensions. I think though that we should do that, and
land in the comm train that leads to TB 52, so that we are forced to
face reality.

Or is someone prepared to argue that we should attempt to maintain
binary extension compatibility in Thunderbird 52?


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