The whole status bar was redesigned, so now you use the area to the left of the address (green, blue, or plain) to check whether the site is secure. [https://support.mozilla.com/en-US/kb/Site%20Identity%20Button Site Identity Button | How to | Firefox Help] Other discussions about this change mention an add-on you can use if you really prefer seeing a lock: [http://support.mozilla.com/en-US/questions/796225 firefox 4 where is the padlock bottom right corner | Firefox Support Forum | Firefox Help] --- By the way, the lock indicates that communications between your browser and the site are encrypted (scrambled) so anyone trying to intercept them will get unintelligible gibberish. It doesn't actually mean that the site is trustworthy or won't leak your information (as recent news stories make all too clear!).