Treestyletab: [Nightly only] Unable to open about:processes after bug 1652785 is fixed

[Fanolian]

Short description

about:processes (Process Manager) is a built-in tool currently available only in Nightly. Recently about:processes stops working when TST sidebar is shown.
Mozregression shows that Bug 1652785 - Show websites loaded in process in about:processes (title, favicon) is the culprit.

* Not to be confused with about:performance (Task Manager) that is available in Firefox Stable.
* A news piece about about:processes: https://www.ghacks.net/2020/05/11/this-is-firefoxs-upcoming-process-manager-aboutprocesses/

Steps to reproduce

1. Start Nightly 2020-09-07 or later with clean profile.
2. Install TST.
3. Make sure TST sidebar is shown.
4. Navigate to about:processes.

Expected result

After a short pause, about:processes should show CPU, memory, etc. information about various Nightly processes.

Actual result

No information is shown. In Browser Console there is an error message after the short pause:

Uncaught (in promise)
Exception { name: "NS_ERROR_FAILURE", message: "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIURI.host]", result: 2147500037, filename: "chrome://global/content/aboutProcesses.js", lineNumber: 208, columnNumber: 0, data: null, stack: "_getDOMWindows/windows<@chrome://global/content/aboutProcesses.js:208:1\n_getDOMWindows@chrome://global/content/aboutProcesses.js:204:35\n_getProcessDelta@chrome://global/content/aboutProcesses.js:280:21\ngetCounters@chrome://global/content/aboutProcesses.js:348:22\n_updateDisplay@chrome://global/content/aboutProcesses.js:904:26\nupdate@chrome://global/content/aboutProcesses.js:891:16\n", location: XPCWrappedNative_NoHelper }

aboutProcesses.js:208

Notes

1. The issues only occurs when TST sidebar is shown. Bookmark, History sidebars are not affected.
2. about:processes works when TST sidebar is hidden, even if TST is still enabled.
3. I tried some older versions of TST (3.3.6+) and they all have the same issue.

Regression range

Last good Nightly: 2020-09-06
First bad Nightly: 2020-09-07
pushlog: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=5a77c0b857048d46fe4bced46b2234b49dcc84a2&tochange=ca131344e7fcf46f50e09bea63141d2578f18b7b

Further bisecting autoland builds:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=0a3de0138b450f7ed71d2ef371c2e8e602a2acaf&tochange=b8af21c6e6780dbca280115d97aa3ae91e7614f4

Environment

• Platform (OS): Windows 10 1909
• Version of Firefox: Nightly 2020-09-07 or later
• Version (or revision) of Tree Style Tab: 3.5.27

[piroor]

Is this already reported to bugzilla.mozilla.org? I think it need to be fixed by Firefox side...

[Fanolian]

Not yet. I'll do it later.

[Fanolian]

Filed: Bug 1665099 - Unable to open about:processes when Tree Style Tab sidebar is enabled.

[piroor]

Thanks!

[Fanolian]

Fixed in 2020-09-19 Nightly.