User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:70.0) Gecko/20100101 Firefox/70.0

Steps to reproduce:

run browser-sync 2.26.7 locally on MacOS Catalina 10.15.1. Using FFDE 70.0b7, go to either internal or external browser-sync URL (localhost:3000), enter webdev inspector and choose Responsive Design mode, click Responsive Design mode icon to exit

Actual results:

enter Responsive Design mode on webdev tools works fine but when try to exit the mode, the tab goes blank and refuses to reload.

Expected results:

dev tools should exit the Responsive Design mode and redraw web page at current desktop browser window size

reverted to FFDE 70.0b5 and Responsive Design mode works as expected

I installed browser-sync and tested the steps described above with both Firefox 72, 71 and 70, but could not reproduce the issue.
The only difference is that I don't have macOS Catalina, only Mojave, but I don't know if that makes a difference.

Just to be sure, here are the steps I took:

• install browser-sync
• start browser-sync with browser-sync start -s -w in a folder where I have some HTML and CSS files for a website
• open firefox on the browser-sync server URL
• open the Inspector
• open RDM
• close RDM again

Gary, does the problem always occur for you? Also, when it does, do you have javascript errors displayed in the browser console (cmd+shift+J)?

javascript console errors upon loading page, entering inspector, entering responsive mode, and then exiting responsive mode

thanks Patrick. It is repeatable on my system with this straightforward HTML/CSS/JS app. Continues to happen in new B9 version of FFDE but not B5.

I added the javascript errors. Looks like it is throwing an exception NS_ERROR_FAILURE