1941006 - Unable to open developer tools

Status: VERIFIED FIXED

(DevTools :: General, defect, P2)

Description

[eight04]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:136.0) Gecko/20100101 Firefox/136.0

Steps to reproduce:

Press F12 or right-click > inspect elements.

Actual results:

An empty window is opened:
https://imgsh.net/i/aedf6664a0

Expected results:

Open the developer tool.

It worked fine after restarting the browser, but broken again after a while.

After closing the empty window, pressing F12 does nothing. There is an error in the browser console (Ctrl-Shift-J):
https://imgsh.net/i/13afe0ebfc

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'DevTools::General' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Julian Descottes [:jdescottes]]

Thanks for the report,

Throwing on the line reported by the browser console doesn't seem to lead to a blank toolbox, so there was probably another error earlier in the logs.

If you have the issue again, can you share more (all?) logs from the browser console?
You can right click on the console and use "Copy all Messages" to do it easily.

Thanks

Comment 3

[eight04]

Happened again when trying inspecting an element. Here is the screenshot of browser console:
https://imgsh.net/i/f0f360aee7
There are thousands of messages since I didn't shutdown my PC for days. The screenshot contains all messages after the right click.

After that, I right-clicked > inspect element and got this error:
https://imgsh.net/i/9616e331d7

Comment 4

[Julian Descottes [:jdescottes]]

Thanks, that helps a bit, although I would be curious to see what failed prior to the watchTargets error message.
You can select "Show timestamps" in the Console settings (top right "Gear" icon), if that can help you select only the logs relevant to the blank devtools issue.

Comment 5

[eight04]

I found the STR:

1. Install LiveTL: https://addons.mozilla.org/zh-TW/firefox/addon/livetl/
2. Disable the extension.
3. Open a youtube live stream e.g. https://www.youtube.com/watch?v=WB2nTzxJ2HQ
4. Restart the browser. Wait for the chat.
5. Right-click on the page -> inspect.
6. The devtools loads correctly. Close devtools.
7. Enable the LiveTL extension.
8. Right-click on the page -> inspect.
9. The devtools doesn't load.

However, I can only reproduce the issue with my default profile. All extensions were disabled except LiveTL.

Tried creating a new profile but can't reproduce.

Comment 6

[eight04]

Attachment: console-export-2025-1-18_15-22-11.txt

Here is the log from browser console.

Comment 7

[Julian Descottes [:jdescottes]]

That's great, thanks for all the details! Hopefully we can track this down now.

Alex: anything interesting in the logs? Given that it seems webextensions related maybe you can spot something here?

Comment 8

[:sorty125]

Attachment: Browser console output when trying to open dev tools

I'm encountering the same issue on 135.0b6. It shows a blank panel when opening dev tools (via F12). The issue doesn't seem to be limited to any one site, however I can get it to happen 100% of the time on https://www.bulkwholesale.com.au/

I've attached the relevant browser console log.

Comment 9

[:sorty125]

I played around with it more and it happens when devtools.debugger.show-content-scripts is true.

Comment 10

[Julian Descottes [:jdescottes]]

Thanks! Putting the bug back to triage to make sure we have some eyes on it this week.

Comment 11

[Alexandre Poirot [:ochameau]]

Thanks a lot :eight04 and :sorty125, I can easily reproduce and fix this issue.

Comment 12

[Alexandre Poirot [:ochameau]]

Attachment: Bug 1941006 - [devtools] Fix DevTools when debugging a page with an extension document used in an iframe.

Comment 13

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/68c18431d3f8
[devtools] Fix DevTools when debugging a page with an extension document used in an iframe. r=jdescottes,devtools-reviewers

Comment 14

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/68c18431d3f8

Comment 15

[Julian Descottes [:jdescottes]]

Should we try to uplift this one?

Comment 16

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1413872

Comment 17

[Alexandre Poirot [:ochameau]]

Comment on attachment 9460471 [details]
Bug 1941006 - [devtools] Fix DevTools when debugging a page with an extension document used in an iframe.

Beta/Release Uplift Approval Request

• User impact if declined/Reason for urgency: DevTools can't be opened on web pages where an extension inserts an iframe with extension document.
• Is this code covered by automated tests?: Yes
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: * toggle devtools.debugger.show-content-scripts to true (can also be toggled from the debugger source tree settings icon)
• Install LiveTL: https://addons.mozilla.org/zh-TW/firefox/addon/livetl/
• Open a youtube live stream e.g. https://www.youtube.com/watch?v=WB2nTzxJ2HQ
• Wait for the chat to appear in youtube. The addon will inject an iframe in the chat.
• open devtools

DevTools will be blank without this patch.

• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): The fix is really naive.
• String changes made/needed:
• Is Android affected?: No

Comment 19

[Ryan VanderMeulen [:RyanVM]]

Comment on attachment 9460471 [details]
Bug 1941006 - [devtools] Fix DevTools when debugging a page with an extension document used in an iframe.

This needs a rebased patch for Beta uplift.

Comment 20

[Alexandre Poirot [:ochameau]]

Attachment: Bug 1941006 - [devtools] Fix DevTools when debugging a page with an extension document used in an iframe.

Bug 1214658 hacks the content script sandboxes to used them for iframes loading
extension documents. These documents expect the privileged chrome/browser APIs,
which are exposed by spawning a content script sandboxes.
These sandboxes won't have any metadata as they don't really are content scripts.
These sandboxes won't execute any script.
They will only be used to expose chrome/browser APIs to these iframes.

Comment 21

[Pulsebot]

https://hg.mozilla.org/releases/mozilla-beta/rev/b021b761658c

Comment 22

[Alexandru Trif, Desktop Test Engineering [:atrif]]

Hello! Reproduced the issue with Firefox 136.0a1 (2025-01-10) on Windows 10x64 by following steps from comment 17. Devtools is blank after opening it.
The issue is verified fixed with Firefox 136.0a1 (2025-01-22) and 135.0b9 (20250122203829) on Windows 10x64, macOS 12 and Ubuntu 24. The dev tools is correctly displayed after following the steps from comment 17.