Thunderbird/Add-ons Guide 63

Add-ons Guide for Thunderbird 63 and beyond

(First Draft)

The picture beyond Thunderbird version 60 is rather uncertain, given the continued high rate of change in Firefox platform code. We will work with add-on authors in the coming months to determine a viable post-60 add-on strategy. Here are some general thoughts.

Work has been undertaken to keep supporting legacy add-ons "somewhat" in Thunderbird 63 and beyond. We implemented an overlay loader that will load XUL overlays for add-ons but may cause graphical glitches or malfunctions. We're tracking this in bug 1476259.

To use this overlay loader, XUL overlay legacy add-ons must replace install.rdf file with a WebExtensions style manifest.json file, which includes the key "legacy" set to true. See Lightning as an example:
https://hg.mozilla.org/comm-central/rev/e81f4b59a00a7d3e18d50fd3851ecbd47762a186#l2.5 (Note: In this changeset the @variables@ are build variables, add-ons need to use fixed strings).
Important: Bootstrapped legacy add-ons continue to work without a manifest.json file and will in fact break if you add that file.

Add-on authors who want to make their add-ons compatible with Thunderbird version from 63 and beyond to version 68 ESR have three options:

• Rely on the mentioned XUL overlay loader. This is only a short-term stopgap solution.
• Make their add-ons restartless, although the replacement for restartless add-ons in TB 68 isn't yet clear. Further reading on restartless add-ons:
  • https://mail.mozilla.org/pipermail/firefox-dev/2018-June/006503.html
  • https://mail.mozilla.org/pipermail/firefox-dev/2018-June/006507.html
  • https://bugzilla.mozilla.org/show_bug.cgi?id=1413432#c7
• Convert their add-on to a WebExtension, using WebExtension Experiments for any API that is not yet provided. This is the preferred approach. You can read more information at https://github.com/thundernest/tb-web-ext-experiments/

Removed in mozilla63

• XUL element listbox together with listboxitem and listcell. -- Replacement: richlistbox.