Responsive Design Mode doesn't work

[Justinh]

In the Dev tools, Responsive Design Mode doesn't work. Use the toggle button or use Ctrl+Shift+M and nothing happens. This is major - anyone know a workaround?

This is broke in the latest version, 2.49.5, but it worked before.

[frg]

I am sure this never worked. There is abug open for it.

https://bugzilla.mozilla.org/show_bug.cgi?id=1284504

++ snip 2.53 +++
Timestamp: 10/2/2019, 10:47:32 AM
Error: A promise chain failed to handle a rejection. Did you forget to '.catch', or did you forget to 'return'?
See https://developer.mozilla.org/Mozilla/J ... sm/Promise

Date: Wed Oct 02 2019 10:47:28 GMT+0200 (W. Europe Standard Time)
Full Message: TypeError: window.gBrowser.getBrowserContainer is not a function
Full Stack: ResponsiveUI@resource://devtools/client/responsivedesign/responsivedesign.jsm:177:20
Manager.openIfNeeded<@resource://devtools/client/responsivedesign/responsivedesign.jsm:84:12
_run@resource://devtools/shared/task.js:311:39
TaskImpl@resource://devtools/shared/task.js:273:3
asyncFunction@resource://devtools/shared/task.js:247:14
toggle@resource://devtools/client/responsivedesign/responsivedesign.jsm:70:7
toggle@chrome://navigator/content/webDeveloperOverlay.js:18:5
oncommand@chrome://navigator/content/navigator.xul:1:1

Source File: resource://devtools/client/responsivede ... design.jsm
Line: 177
Source Code:
177