I use Firefox 60.8.0esr-1~deb10 which is a package in Debian 10.0 (stable).
I have had the following problems with Firefox for several days. ==== The following problem suddenly went away today. I did not do anything. But History Cleaner was last updated on August 9, 2019. Today! I go to the page: https://addons.mozilla.org/en-US/firefox/addon/history-cleaner/?src=search I click on "+Add to Firefox". A small box appears at the top. I click on "Add". It hangs. The browser console says: "PopupNotifications._onButtonEvent: Button click happened before the window was focused" The "Cancel" option in the box also fails. ==== Click "Help", then click "Troubleshooting information". A few lines down is a box that says "Open Directory". Nothing happens when I click on the box. ==== Go to the Refresh Firefox page at: https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings There is a box saying "Refresh Firefox". Clicking on the box does nothing. Thanks.