Ubuntu Firefox 53.0+build6 with clean profile, Ubuntu Modifications add-on only: same bug as reported above
Ubuntu Firefox 53.0+build6 with clean profile and no add-ons: same bug as reported above
Ubuntu Chromium 58.0.3029.96: same bug as reported above
Linux 64bit Official Mozilla Firefox 53.0.2 with clean profile: no problem
Windows 32bit Mozilla 52.0.2: no problem
This implies it's an Ubuntu-specific issue. Didn't realise they made any substantive changes. Shall I file a bug in Canonical Launchpad?
Good idea. I've retested, results are as follows:
Ubuntu Firefox 53.0+build6 with clean profile, Ubuntu Modifications add-on only: same bug as reported above
Ubuntu Firefox 53.0+build6 with clean profile and no add-ons: same bug as reported above
Ubuntu Chromium 58.0.3029.96: same bug as reported above
Linux 64bit Official Mozilla Firefox 53.0.2 with clean profile: no problem
Windows 32bit Mozilla 52.0.2: no problem
This implies it's an Ubuntu-specific issue. Didn't realise they made any substantive changes. Shall I file a bug in Canonical Launchpad?