Removal of XUL/XBC(?XPCOM? from m-c? WAS Re: What happened to hiring an architect?

Magnus Melin mkmelin+mozilla at
Wed Dec 21 20:43:13 UTC 2016

Like aleth wrote, there have been no announcements about removing 
XUL/XBL. XUL is deprecated, meaning Mozilla will not put any effort on 
moving if forwards (patches NOT accepted!). XUL in add-ons is going away 
for Firefox Add-ons, but will live on in Firefox/Thunderbird core for 
who knows how long. Removal is only a long term goal, so I would not be 
surprised if it's still used 10 years from now, but these things are 
hard to predict.

XPCOM is not deprecated, and the implications would be massive. It would 
happen way in the future if ever.

So, removal is not imminent but that doesn't mean there aren't a lot of 
rewriting into web technologies that should happen as soon as possible, 
since that is not such a moving target, pool of contributors is 
potentially huge and there would eventually be a possibility of a 
version for mobile.


On 21.12.2016 16:08, Disaster Master wrote:
> On 12/15/2016 5:00 PM, aleth at <aleth at> 
> wrote:
> > I'm not aware of any timetable for removing XUL/XBL from m-c. What *has*
> > been announced is the depreciation of non-webextension addons in Firefox
> > from Firefox 57 onwards
> Ok, this will likely be my next to last post in this thread, but this 
> is a really critical point that I neglected to pursue.
> (I have another reply to address the question of a total rewrite - and 
> I honestly like the idea)
> First, no one responded to my question about XPCOM with respect to the 
> above.
> So - _*is XPCOM included with XUL/XBC in the above comment?*_
> Assuming it is, here is another important question.
> _*Is it the removal of XUL/XBL(/XPCOM) from m-c that poses the 
> imminent threat to TB, both from a UI and Addon perspective?*_
> If the answer is no, then I guess you can ignore what follows, 
> although I would appreciate comments about the relevance of the above 
> comment from Andrew.
> If, the answer is a partial yes, then I guess which parts determines 
> how much of what follows is relevant, and I would appreciate comments 
> to that effect.
> If, however, the answer is *yes* in full, then it seems to me there is 
> a huge glaring question that needs to be pursued with the folks at 
> Mozilla.
> Is there anyone here that can actually pursue this with someone at 
> Mozilla, and get some kind of meaningful answer - or if none is to be 
> had right now, at least start a ball rolling to develop a meaningful 
> answer to this question:
> _*How long before XUL/XBL(/XPCOM) will actually be slated for removal 
> from m-c? Is it possible to even get a rough estimate of a date?*_
> If XPCOM is not included in the above, then this same question just 
> needs to be asked about XPCOM too, since TB apparently relies just as 
> heavily on it as XUL/XBL.
> The answer could have a huge impact on our strategy, both immediate 
> and long term. E.g., if it won't happen for at least another 5+ years, 
> we might take a very different direction than if the answer is a more 
> definite shorter time-frame (1? 2? 3?).
> They should stress just how important it is to the TB devs to get some 
> kind of an idea of the answer - as well as notifications to 
> appropriate people on the TB council if anything changes going forward 
> - in order for us to devise an effective strategy for handling this 
> eventuality.
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