Some settings for Firefox cannot be adjusted in the normal way (via the “Settings” menu item).
Remove service workers
Open about:debugging#/runtime/this-firefox in the address bar.
Delete all listed service workers by enteringfor (let button of document.querySelectorAll(".qa-unregister-button")) { button.click(); }
in the debugger console.
More than 4 rows of top sites on start page
Open about:config in the address bar.
Enter browser.newtabpage.activity-stream.topSitesRows in the search field.
Enter the desired number of rows.
Keep backspace key from going back to previous page
Open about:config in the address bar.
Enter browser.backspace_action in the search field.
Set the value to 2 to unmap the backspace key.