XUL Overlays Removed
Brendan Dahl
This is hopefully the last thing you’ll ever hear about XUL overlays as they have now been completely removed from Firefox[1]. For those unfamiliar with overlays, they provided a way to merge two XUL documents and were mainly used by legacy extensions and in several places within the Firefox UI. While overlays served a purpose, they were removed since we no longer support legacy extensions and they added unneeded complexity to Firefox.
Removing overlays cut around 3.5K lines of code from Firefox and in my opinion made understanding which resources get loaded into which documents easier to reason about (see one example of a before[2] and after[3] below). This is just one piece of the broader XUL removal effort, but it does highlight that things can be simpler in a post-XUL world.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1426763
[2] https://bug1441378.bmoattachments.org/attachment.cgi?id=8954951
[3] https://bug1441378.bmoattachments.org/attachment.cgi?id=8954952
Key:
Arrow direction: where elements go from -> to.
Red: MacOS only
Green: Non-MacOS
Blue: where the <overlay> element went
Kris Maglione
>This is hopefully the last thing you’ll ever hear about XUL overlays as
>they have now been completely removed from Firefox[1].
\o/ Thank you to everyone who was involved in this!
>Removing overlays cut around 3.5K lines of code from Firefox and in my
>opinion made understanding which resources get loaded into which documents
>easier to reason about
I completely agree. I can't count the number of times I've made
a change in one place that seemed obviously sound, only to have
it break on try because some completely unrelated piece of code
loads a special overlay into the window only on OS-X.
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