An end user was complaining of slowness in Gmail using Safari on the Mac. After taking a look around, quitting and re-opening, and trying a couple items found online, I noticed that there were a number of tabs open in another browser window.
It turned out that the re-open tabs on startup was causing him to end up with Gmail open in more than a dozen tabs at a time. In addition, he was moving between Google Drive, Calendar, and Gmail using the black bar at the top of the screen rather than cycling between browser windows to find the one that was already open, which was opening additional windows. With each window he opened, Gmail got even slower.
The solution was to close any extra Gmail windows in the background, and help the user use the "Window" menu to find Gmail rather than re-opening it each time he wanted it open. I also disabled the "reopen windows at login" to keep it from starting up with more than a dozen instances each time after he shuts down.
