@JayOpera I found how to make the tabs and address bar disappear while watching videos in full screen mode.
- Open two tabs.
- Go to YouTube or Prime Video on one tab.
- Switch the video to full screen mode. The tabs and address bar will be visible now.
- Close the another tab. Now, the tabs and address bar will be disappear.
- If you want to open a new tab or to access the address bar, press 'Command+T'. To go to the full screen mode again, follow the same steps above.