Closed Bug 1247640 Opened 5 years ago Closed 3 years ago

Sending a synchronous message from nsIContentPolicy.shouldLoad() causes drawing issues on Restore Session page


(Firefox :: Extension Compatibility, defect)

Not set



Tracking Status
firefox47 --- affected


(Reporter: ecfbugzilla, Unassigned)




(1 file)

Steps to reproduce:

1. Change xpinstall.signatures.required preference to false and install attached extension (minimal testcase distilled from Adblock Plus, does nothing beyond registering a content policy in all processes and sending a synchronous message from nsIContentPolicy.shouldLoad()).
2. While Firefox is running, make a copy of sessionstore-backups/recovery.js file in the Firefox profile.
3. Close Firefox.
4. Restore your copy of sessionstore-backups/recovery.js and replace sessionCheckpoints.json file in the Firefox profile by the following:

> {"profile-after-change":true,"final-ui-startup":true}

5. Start Firefox again.

Steps 2-4 can be replaced by crashing Firefox.

Expected results:

Session Restore page shows up saying "Well, this is embarrassing" and offering you to restore the previous session. Close and Restore buttons are visible under the list.

Actual results:

50% of the time the Close and Restore buttons won't be visible for me (Firefox 47.0a1 nightly from 2016-02-11 on OS X 10.11, issue was originally reported for Firefox 45.0a2 aurora on Windows 10). Resizing the browser window or moving the mouse over the buttons makes the buttons appear.

Unfortunately, I was unable to reproduce the issue with an exact copy of about:sessionrestore in an extension, so I was unable to narrow this down further.
We worked around this issue in Adblock Plus (, this change will be part of the Adblock Plus development build as well as Adblock Plus 2.7.2 on February 23.
Closed: 3 years ago
Resolution: --- → WONTFIX
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