Upcoming changes to frame scripts

Johann Hofmann jhofmann at mozilla.com
Thu Aug 9 06:42:11 UTC 2018

Hi Felipe,

thank you for working on this, generally this seems like great progress to

I have one slight concern: if I understand correctly, we are aiming to
remove the ability for chrome-privileged JS to inject frame/content scripts
on the fly, right? I'm currently working on a Shield study which uses a
privileged frame script to extract information from the content process it
would otherwise not have access to. I have seen other Shield studies use
frame scripts as well.

Am I right in assuming that future studies would need to land IPDL
boilerplate in m-c to achieve something like this?

Thank you!


On Wed, Aug 8, 2018 at 9:42 PM Felipe G <felipc at gmail.com> wrote:

> Hello firefox-dev!
> If you’ve ever written code inside of a frame script, and communicated
> with it over a message manager, you’re going to want to pay close
> attention, because the world is about to change.
> Over the past couple of months we’ve been splitting most of the code from
> frame scripts into .jsms to load them on demand. We’ve been doing this to
> improve content process memory consumption as part of the Fission effort,
> and have been doing this mostly in an ad-hoc way. Bug 1472491 [1] is
> creating a general structure to solve this class of problem, and moving
> most of the frame scripts code to this new structure.
> In short, the messages/listeners/observers will be listed in a declarative
> way, specifying which module should be loaded and instantiated to respond
> to these messages.
> These modules are classes exported from these .jsms, extending an
> ActorChild class, which has access to the document, the docshell and the
> message manager. Now you should access them through the class instead of
> the globals in the frame script. A good example: [2]
> In order to spread knowledge about this change, we’ll be spreading the
> reviews from bug 1472491 to several people so that everyone can look at
> their corresponding areas of the code and see what the changes look like.
> Let us know if you have any questions or concerns!
> Also, a note: in a not-so-distant future, the frame scripts are likely to
> be fully phased out, and once the JS IPDL API is ironed out (Bug 1475415),
> the messages sent through the message manager will be replaced by real IPC
> messages.
> [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1472491
> [2] https://reviewboard.mozilla.org/r/260636/diff/1#index_header
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