When starting Firefox 63, if you have a clean or new profile, pressing Ctrl+Tab displays all open tabs by default.
Like Windows, which shows thumbnail previews of open apps when you press Alt+Tab, Mozilla has introduced a preference browser.ctrlTab.previews in about:config in Firefox 4, which when enabled shows the thumbnail preview of the tabs in the center of the browser window.
Ctrl+Tab Previews enabled by default in Firefox 63
The company added the UI option Ctrl+Tab cycles through tabs in recently used order for tabs under General in Options for Discovery in Firefox 50. The option is disabled by default. After removing the option to never check for updates, the Firefox team enabled Ctrl+Tab views by default for Firefox browsers for new profiles, this change takes effect in Firefox 63.
error 1473595-Enable “Ctrl+Tab cycles through tabs in most recently used order” feature by default in new profiles.
Behind the scenes, Firefox sets the following about:config preference values to true.
If you don’t like the change, you can disable Ctrl+Tab views in Firefox, here’s how.
Disable Ctrl+Tab Views in Firefox
1. Click on the menu
2. Select Options > General > Guides
3. Uncheck ‘Ctrl+Tab cycles through tabs in most recently used order’.
READ: Firefox 63: Disable Quick Find (for ‘ and / keys)