I can't reproduce your issues 1 and 2. You can reinstall an older version if it works better for you: https://addons.mozilla.org/en-US/firefox/addon/enhancer-for-youtube/versions/

For issue 3, check under Options > Appearance > Hide comments (maybe you enabled it by inadvertence)

For issue 4, not tested but it must be due to how Firefox loads extensions on restart.