User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Firefox/38.0 Build ID: 20150525141253 Steps to reproduce: opened private window Actual results: there is no indication that it is private browsing mode. Expected results: ourple mask icon in the top right corner
Have you tried if you see this issue in a new profile, too? You can find details on how to create a new profile (without changing anything in your regular profile!) at https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles . Have you tried if you see this issue in Firefox's safe mode, too? You can restart Firefox into safe mode by using the 'Restart Firefox with add-ons disabled' entry in the 'Help' menu. This will also disable graphics hardware acceleration and some JS engine optimizations, not just extensions and plugins. See https://support.mozilla.org/kb/troubleshoot-firefox-issues-using-safe-mode .
Launching Firefox with the private browsing flag set on the command line: Windows: firefox.exe /private Linux: firefox -private brings up Firefox in private browsing mode, but without the purple mask icon in the tab bar for all private browsing pages. The default "You're browsing privately" page has a mask icon in its tab, probably a favicon, but other pages do not. If you launch Firefox with, for example firefox.exe http://www.example.com /private or firefox http://www.example.com -private Firefox comes up in private browsing mode, with no visible indication of the fact. If Firefox is started with a Windows startup item with the /private flag, (not unusual for public-access computers), this situation can arise. (Because private browsing disables many add-ons, I spent several days chasing a problem reported with one of my add-ons before discovering this. The reporting user didn't know they were in private browsing mode.)
Per comment #2, marking this as a duplicate of the same issue as filed earlier.