Proposal: MailExtensions API to allow UI overlays, but no script injection

ace acelists at
Sat Oct 12 10:55:46 UTC 2019

Dňa 12. 10. 2019 o 0:20 Eyal Rozenberg napísal(a):
> On 12/10/2019 1:08, Geoff Lankow wrote:
>> but having the ability to change any window and do anything to it /can
>> not/ and /should not/ continue.
> Why? That is a keystone feature of Thunderbird's - the fact that UI from
> an extension code is basically on equal footing with in-app UI.

Hi. We recently added a feature in Thundebird that allows addons to
listen when specific windows are opened (by specifying document URLs
they are interested in). When that happens, the addon specified code can
run on that window. Then you could change the appearance of UI elements
using standard DOM methods, instead of a XUL overlay file.

See registerWindowListener() at

This could cover some of the addon use-cases.


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