Now add this "forem" to your sidebar, you can because the plus sign allows it.
Reload and you should get this error
Error handling response: TypeError: Cannot read property 'homePageUrl' of null
at chrome-extension://kbbmmajekblbmamcpkopjkmihmddkpof/content/content.js:207:14
at Array.map (<anonymous>)
at myOrigins (chrome-extension://kbbmmajekblbmamcpkopjkmihmddkpof/content/content.js:206:19)
at chrome-extension://kbbmmajekblbmamcpkopjkmihmddkpof/content/content.js:14:18
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Using mac + chrome
I eventually got it to work by uninstalling the old version, reinstalling the source and hard refreshing the pages.
I think I also managed to get it into an unusable state. This is how it may be reproduced: