Macbook Air connected, but not displaying properly on tv

I had a lot of trouble with Airplay & mirroring to tv (signal kept dropping & wouldn't reconnect), so I bought a cable. Yesterday I had no trouble watching several hours of streaming video using the Firefox browser. Today the tv is showing me the Macbook wallpaper, so there is a connection, & sometimes it shows the Weather app & another window that I leave open always, but it will not show my internet browser at all. It will not show the dock or the cursor. The screen of the Macbook doesn't look at all like what's showing on the tv. I've restarted everything a couple times, unhooked & hooked back up, looked at all the settings I can think of, & I cannot figure out what has changed since yesterday. Has anyone run into this? I couldn't find anything in the Help topics either. Thanks for any helpful help.