I happened across this Aug3,'14, for my Fox Fire always disappearing when minimized and ending up with lots of extra open browser windows from clicking on the icon thinking it was how to open /maximize to the screen at prior size-not full screen. I am using Mint 17 MATE and the process is a bit different to get the Add to panel list, but right clicking on a nearly invisible icon of 4 or so horizontal dash marks on the panel that look just like the notification area icon but this opens up the has 'preferences' in the list with 'lock','move' and those. There are 2 more of the exact same appearing icon or whatever that only have 'help' remove, about and lock or move. nothing else. i think they are all notification area icons only one has preferences and one running app, or applet thought there are a number actually running and showing. do not get it. but that is how it works in this panel in this installed version of MInt 17 Qiana, Mate that otherwise functions fairly well. Only been using linux about 5weeks today and only used mate, cinnamon and the live cd downloads i tried out for ubuntu, kbuntu 4 in 1 live i didnt use in 12.04 and then the recent Trusty 14.04. for me, Mint was the best, easiest to learn on others were fine but a bit more steep learning curve, i though in the first week of practice.
Thanks for this tip, did do something. I found 2 window switcher applets i have put in the panel. now, at least, i do not need to do the Alt-Tab to flash up the running apps or windows and open one at a time that way. was too hit or miss and a mouse click is sometimes faster than needing a keyboard to push down a few/couple of keys.
Though the solution right click on panel is the best way , on the proper part of some panels , i guess, the add to panel did not show up, it will though
just my 2¢ in case someone else has a problem through inexperience as I did.