Bug: TB mochitest: JavaScript Error: "TypeError: can't access property "length", this._l10nButtons is undefined" {file: "chrome://global/content/elements/dialog.js" line: 324}
Status: NEW
Priority: --
Created: 2021-11-08 14:03:00+00:00
Resolved: 2022-03-18 10:08:08+00:00

A couple of tests generated this error.
I noticed them in my local log when I ran DEBUG version of TB during mochitest.

They are also present on linux64 debug test on try-comm-central.
See for example,
https://firefoxci.taskcluster-artifacts.net/IYzJg6CZSqO3qW0IBY_kQg/0/public/logs/live_backing.log
The above is from Geoff's job.: https://treeherder.mozilla.org/jobs?repo=try-comm-central&revision=282a50bcb1aff3b343501350c5731bf19d19327c

So they are for real, not caused by my local patches.

Following the excerpt from local log. The test name and the local stacktrace.

```
92:03.75 TEST_START: comm/mail/test/browser/composition/browser_attachmentReminder.js
92:28.41 GECKO(622306) JavaScript error: chrome://global/content/elements/dialog.js, line 324: TypeError: can't access property "length", this._l10nButtons is undefined
92:28.45 INFO Console message: [JavaScript Error: "TypeError: can't access property "length", this._l10nButtons is undefined" {file: "chrome://global/content/elements/dialog.js" line: 324}]
postLoadInit@chrome://global/content/elements/dialog.js:324:11
MozDialog/<@chrome://global/content/elements/dialog.js:61:53
openWindowPrompt@resource:///actors/PromptParent.jsm:161:19
receiveMessage@resource:///actors/PromptParent.jsm:108:21
openPrompt@resource://gre/modules/Prompter.jsm:1182:36
openPromptSync@resource://gre/modules/Prompter.jsm:1046:10
alert@resource://gre/modules/Prompter.jsm:1329:17
fail@resource:///modules/MessageSend.jsm:335:35
_deliveryExitProcessing@resource:///modules/MessageSend.jsm:606:12
sendDeliveryCallback@resource:///modules/MessageSend.jsm:671:17
OnStopRunningUrl@resource:///modules/MessageSend.jsm:1305:19
sendMailMessage/client.onerror@resource:///modules/SmtpService.jsm:187:41
_onError@resource:///modules/SmtpClient.jsm:442:10
waitFor@resource://testing-common/mozmill/utils.jsm:111:12
waitForModalDialog@resource://testing-common/mozmill/WindowHelpers.jsm:389:11
wait_for_modal_dialog@resource://testing-common/mozmill/WindowHelpers.jsm:647:17
click_send_and_handle_send_error@chrome://mochitests/content/browser/comm/mail/test/browser/composition/browser_attachmentReminder.js:806:24
test_attachment_reminder_dismissal@chrome://mochitests/content/browser/comm/mail/test/browser/composition/browser_attachmentReminder.js:227:35
...
121:41.01 TEST_START: comm/mail/test/browser/folder-display/browser_messageCommandsOnMsgstore.js
121:59.69 GECKO(627867) JavaScript error: chrome://global/content/elements/dialog.js, line 324: TypeError: can't access property "length", this._l10nButtons is undefined
122:00.03 INFO Console message: [JavaScript Error: "TypeError: can't access property "length", this._l10nButtons is undefined" {file: "chrome://global/content/elements/dialog.js" line: 324}]
122:00.03 INFO Console message: [JavaScript Error: "TypeError: can't access property "length", this._l10nButtons is undefined" {file: "chrome://global/content/elements/dialog.js" line: 324}]
postLoadInit@chrome://global/content/elements/dialog.js:324:11
MozDialog/<@chrome://global/content/elements/dialog.js:61:53
sleep@resource://testing-common/mozmill/utils.jsm:62:12
enter_folder@resource://testing-common/mozmill/FolderDisplayHelpers.jsm:464:14
be_in_folder@resource://testing-common/mozmill/FolderDisplayHelpers.jsm:502:17
subtest_check_queued_message@chrome://mochitests/content/browser/comm/mail/test/browser/folder-display/browser_messageCommandsOnMsgstore.js:219:15
reply_forward_message@chrome://mochitests/content/browser/comm/mail/test/browser/folder-display/browser_messageCommandsOnMsgstore.js:258:9
test_mark_messages_replied@chrome://mochitests/content/browser/comm/mail/test/browser/folder-display/browser_messageCommandsOnMsgstore.js:275:9
Tester_execTest/<@chrome://mochikit/content/browser-test.js:1091:34

122:29.03 TEST_START: comm/mail/test/browser/folder-display/browser_messagePaneVisibility.js
```