Report 2 problems related to Firefox extension development

wei_huang at wei_huang at
Tue Nov 7 07:33:12 UTC 2017

Hi Mike and Luca

Thanks a lot for your answer and advices!

For issue #2, I’ve just tried to find if there are any exceptions when loading defined content script js, but seems no exception.

As shown in content_script_def.JPG, I want to load Temp1.js and 4 other jses when accessing Facebook setting page.
But seems all the js defined in this block are not injected into the target page. (see content_scripts.png)

The manifest.json and some other related files are appended. (the jses are renamed to .txt files, in case be blocked by browser security policy)

l  All the content scripts defined in other blocks are injected normally, such as the one for matching "*://*";

l  As I mentioned before, the problem only exists on signed xpi. If load extracted xpi or local code, no such issue.

If any questions, please feel free to let me know.


From: Mike Lissner [mailto:mike at]
Sent: 2017年11月7日 1:32
To: Luca Greco <lgreco at>
Cc: Wei Huang (RD-CN) <wei_huang at>; dev-addons at
Subject: Re: Report 2 problems related to Firefox extension development

Am I understanding correctly that if one content script has, say, a syntax error, it just won't show up in the debugger, and it also won't throw an error except in the "browser console"?

And if the script throwing the error is the first script in the manifest array, then the entire extension won't show up in the debugger?

This explains a lot of frustration I've had if so. Things fail, and there's no error that I see telling me what happened. On top of this, I get random errors from jse files in my console that are just confusing and unrelated to me. Are we expected to be watching both the browser console, and the webcontext console at the same time? While we watch, are we expected to filter out the messages that are relevant to us, and ignore the rest somehow — that's annoying? Is the browser console available from Tools > Browser Console the same thing as the console you get in the debugger for the extension's background page? If it's different that makes three debuggers we have to watch.

Two was already a lot, and this gets at another deep frustration I've had developing my webextension: I have to have two debuggers and consoles open and I need to watch them both. There's gotta be a better way to do this. It causes lots of trouble:

 - I think a debugger paused. Which one? (this is compounded by the debugger not always being green when paused)
 - I think I need to add a breakpoint in my code...which debugger should it go in?
 - I'm going to have my code log to the console...which console should I watch for it? (We had a new dev spend an hour trying to figure out why a console.log() wasn't logging anything. The answer? He needed a second debugger open, something he could hardly imagine.
 - OK, I read that important email from the boss and now I need to get back to work...I have three browser windows to choose from instead of two (①My regular browser (research and whatnot), ② The browser for debugging the context script with the webpage loaded in it, and ③ the debugger for the background page). This is confusing and annoying and slows down development.

Some of this is probably my fault, not knowing the difference between a browser console, a background page console, and a webcontext console, or whatever. But...frankly...I'm convinced this sucks, and people need to be guided to the right path of doing this, or we need a better way, so people like me can't go wrong.

The backend for my extension logs how many requests it gets. I crossed 1,000 debugging requests over the weekend. That's an unbelievable number of requests to make for a fairly simple extension. I'm not a JS guy, but I was and am shocked at how much effort this is taking. 1,000 debug requests to the backend for one extension. 1,000!


On Mon, Nov 6, 2017 at 8:43 AM Luca Greco <lgreco at<mailto:lgreco at>> wrote:
On Mon, Nov 6, 2017 at 12:48 PM, wei_huang at<mailto:wei_huang at> <wei_huang at<mailto:wei_huang at>> wrote:
Dear Mozilla support team

This is Wei Huang, a FF extension developer.

I’m writing this mail to ask for your help on 2 problems I encountered recently.

[Basic Information]
Firefox Version:
(1).Firefox Release Edition  56.0.2 (32-bit)
(2).Firefox Dev Edition 57.0b14 (64-bit)

[Problems Description]
#1. I happened to find that 2 strange js files, which are not belong to my extension, were injected with the content script jses of my extension. (Refer to attached #1.png)
I’m wondering what are these jses used for? Are there any impact to my extension?

Every extension has its own content script sandbox, and so the content scripts that are not part of your extension
are not injected in your extension content script sandbox, but there is definitely an issue to fix on the debugger UI side,
which doesn't currently show the extension uuid in the left sidebar outline and so it is not currently clear enough which is the related extension
(the extension uuid is only partially visible when hovering with the mouse the filename on the opened source tabs).

#2. Some content script files defined in manifest.json are not injected into target web page.
As shown in #2_1.jpg & #2_2.jpg, when accessing Facebook setting page(, all the jses that match "*://**<*>" should be injected.
However, most of these content script files are missing on this page.
One interesting thing is that, the #2 issue only happens on signed xpi. When I extract the xpi, and load a temporary extension in debug mode, the issue is improved.
I have no idea what’s going on with this issue.

If the file is not listed in the debugger panel, there could be a loading error (which should be listed in the Browser Console, Bug 1410932 aims to make this kind of errors visible in the tab developer tools as well).

If there is no loading error related to the extension, it could be worth to investigate if the extension content scripts have been loaded and
they are just not listed in the Debugger UI, e.g. by temporarily adding a new content script url at the end of the content scripts js array
which just produces a "console.log" message (because the content scripts are loaded in the same order of the js array in the content_scripts manifest property and,
at least currently, if any of the script fails to load then all the subsequent scripts are not going to be loaded).

Dev-addons mailing list
Dev-addons at<mailto:Dev-addons at>
Mike Lissner
Executive Director
Free Law Project


This message has been analyzed by Deep Discovery Email Inspector.

<table class="TM_EMAIL_NOTICE"><tr><td><pre>
The information contained in this email and any attachments is confidential 
and may be subject to copyright or other intellectual property protection. 
If you are not the intended recipient, you are not authorized to use or 
disclose this information, and we request that you notify us by reply mail or
telephone and delete the original message from your mail system.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: content_scripts.png
Type: image/png
Size: 141602 bytes
Desc: content_scripts.png
URL: <>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: content_script_def.JPG
Type: image/jpeg
Size: 32765 bytes
Desc: content_script_def.JPG
URL: <>
-------------- next part --------------
A non-text attachment was scrubbed...
Type: application/x-zip-compressed
Size: 34005 bytes
URL: <>

More information about the Dev-addons mailing list