Separate Security issue please update your Flash 25.0 r0 https://get.adobe.com/flashplayer/ Current version is 30.0.0.113

Hi, there are all sorts every where. The 3 Bar hamburger menu at the far right side in line with your extensions or the address bar.

Or mouse to the top of the browser to a empty spot and Right Click and turn on the Menu Bar.

Let us know if need further help.

Try using Preferences.

See also:

• https://support.mozilla.org/en-US/kb/Options+window

Do you use the Firefox 52.8.0 esr version from the Ubuntu repositories?