To get it to be automatically full screen without having to edit each time, just save the full address including values in your bookmarks bar.
Right click bookmarks bar in a space such as the empty grey space after the last bookmark to the right -> add page ->
Name: Arcane Legends
URL: http:// account.spacetimestudios.com/arcanelegends /?w=1366&h=768 (the version with your values obviously if theyre diff from mine :P)
Once saved, if you can't see the bookmark on the bar, click the little double arrow like this " >>" which is to the far right of the bar, find your new bookmark at bottom of list and drag it onto the bar to the position where you want it.
Then don't load from Apps, just click it in the bookmarks bar and it will load that way everytime.
This is how I do it and it absolutely does not make me redownload anything ever except when there is an actual patch (and I've been playing this way since just before Ursoth event... nothing strange has ever happened whatsoever period )
Bookmarks