Bugzilla

I've investigated a little what happens. Things I've confirmed:

* This happens only on macOS.
* This happens with these steps:
  1. Start Nightly with a clean profile.
  2. Go to about:preferences and configure Nightly to restore previous session on the startup. (Now you have two tabs in the window: the initial tab and the about:preferences tab.)
  3. Press Command-N to open a new blank browser window. (Now you have two browser windows.)
  4. Type "Tree Style Tab" into the address bar and hit the Enter key, to search it on the Web.
  5. Go to the addon page and install TST.
  6. Press Command-T to open a new blank tab. (Now you have two tabs in the window: TST addon page and a blank tab.)
  7. Exit Nightly.
  8. Start Nightly. Now you have two browser windows with opened sidebars.
  9. Exit Nightly.
  10. Start Nightly. Now you have two browser windows, one has opened sidebar but another has closed sidebar. (The problem happens.)
  11. Type "Second Search" (or something another addon which requires "tabs" permission) into the address bar and hit the Enter key, to search it on the Web.
  12. Go to the addon page and install Second Search.
  13. Go to about:debugging.
  14. Open the inspector of the Second Search.
  15. Go to the "Console" tab.
  16. Run `browser.tabs.onHighlighted.addListener(console.log)`.
  17. Try to switch tabs on both windows. You'll see notified events only around events on the second window.
* As described above, the problem affects to other addons. When this happens, Firefox does not notify events around the first window to browser.tabs.onXXX listeners of any addons no only TST.
* I've tried a small testcase instead of TST but the problem does not happen. TST's initialization process calls large number of APIs, so some of them may trigger the problem.

Anyway there looks to be a bug of Firefox itself because the problem affects to other addons also. The WebExtensions system need to isolate each addon and the problem must be enclosed only to TST.

I've investigated a little what happens. Things I've confirmed:

* This happens only on macOS.
* This happens with these steps:
  1. Start Nightly with a clean profile.
  2. Go to about:preferences and configure Nightly to restore previous session on the startup. (Now you have two tabs in the window: the initial tab and the about:preferences tab.)
  3. Press Command-N to open a new blank browser window. (Now you have two browser windows.)
  4. Type "Tree Style Tab" into the address bar and hit the Enter key, to search it on the Web.
  5. Go to the addon page and install TST.
  6. Press Command-T to open a new blank tab. (Now you have two tabs in the window: TST addon page and a blank tab.)
  7. Exit Nightly.
  8. Start Nightly. Now you have two browser windows with opened sidebars.
  9. Exit Nightly.
  10. Start Nightly. Now you have two browser windows, one has opened sidebar but another has closed sidebar. (The problem happens.)
  11. Type "Second Search" (or something another addon which requires "tabs" permission) into the address bar and hit the Enter key, to search it on the Web.
  12. Go to the addon page and install Second Search.
  13. Go to about:debugging.
  14. Open the inspector of the Second Search.
  15. Go to the "Console" tab.
  16. Run `browser.tabs.onHighlighted.addListener(console.log)`.
  17. Try to switch tabs on both windows. You'll see notified events only around events on the second window.
* As described above, the problem affects to other addons. When this happens, Firefox does not notify events around the first window to browser.tabs.onXXX listeners of any addons not only TST.
* I've tried a small testcase instead of TST but the problem does not happen. TST's initialization process calls large number of APIs, so some of them may trigger the problem.

Anyway there looks to be a bug of Firefox itself because the problem affects to other addons also. The WebExtensions system need to isolate each addon and the problem must be enclosed only to TST.