Some additional devtools improvements in about:newtab#asrouter to help with testing different templates and verifying content from different providers: A way to enable/disable providers via the UI; A way to filter the messages shown by provider; A way to reset the preference via the UI Testing instructions 1. Turn on devtools by setting browser.newtabpage.activity-stream.asrouter.devtoolsEnabled to true 2. Visit about:newtab#asrouter 3. Try enabling/disabling different providers; see if their messages show up/disappear on the page 4. Try the messages filter dropdown under the "Messages" section 5. After changing some settings, try the "Restore defaults" button and ensure browser.newtabpage.activity-stream.asrouter.messageProviders is the default value in about:config

Commit pushed to master at https://github.com/mozilla/activity-stream https://github.com/mozilla/activity-stream/commit/663a09ecb22f7af6e447970d659753e6db0a166f Fix Bug 1500073 - Add enable/disable/reset devtools for ASRouter

I have verified this issue with the latest "Firefox Nightly" build (64.0a1 - Build ID 20181022100055) installed, on Windows 10 x64, Arch Linux and Mac 10.13.3, and I can confirm the following: 1. The messages can be enabled/disabled from the "Message Providers" area (all except the "snippets_local_testing" ones; 2. The messages can be filtered from the dropdown displayed under the "Messages" section; 3. The "browser.newtabpage.activity-stream.asrouter.messageProviders" pref is reset to its default value after the "Restore defaults" button is pressed.