I determined the file https://searchfox.org/comm-central/source/mail/components/devtools/devtools-loader.js is missing from the omni.ja file of a packaged TB distribution (official releases from server). When I added the file, the click started working. The file was added in bug 1279834. It exists when building locally, but isn't included in the packaged application version. I also tested 'mach package' locally which resulted in the same problem. There are a few other files similarly missing in the omni. js .
Bug 1427590 Comment 18 Edit History
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I determined the file https://searchfox.org/comm-central/source/mail/components/devtools/devtools-loader.js is missing from the omni.ja file of a packaged TB distribution (official releases from server). When I added the file, the click started working. The file was added in bug 1279834. It exists when building locally, but isn't included in the packaged application version. I also tested 'mach package' locally which resulted in the same problem. There are a few other files similarly missing in the omni.ja.