If you get the error "Firefox already running but not responding" when you turn on Firefox, there are a few fixes you should take. Start by restarting your computer, disabling Firefox using task manager and check if you have permissions to enable Firefox.
Mozilla Firefox keeps a record of all the files you download, so you can easily find them again later. However, if you want to keep your download history private, or if you're just trying to clean up the mess, you can clear it.
To fix Chrome not playing videos you need to: restart chrome, clear temporary data, check your internet connection, enable Java Script, disable Hardware Acceleration or reset your browser to factory settings.
To enable incognito mode on almost any device, you need to click on the three buttons at the top right of the Chrome browser. In the drop-down window, select the option that opens a new tab in Incognito mode.