in Windows you can access from Start / Programs / Mozilla Firefox / Mozilla Firefox (Safe Mode). Or we can make it through Start-> Run and in the window that appears we paste the following path"C: Files programaMozillaFirefoxfirefox.exe" -safe-mode.
In GNU / Linux, if Firefox is in the path and use KDE or GNOME, just press Alt + F2 and type "firefox -safe-mode" or "mozilla-firefox -safe-mode", it depends how you have it. Of course, you can also do the same from a terminal.
On Mac OS X route will /Applications/Firefox.app/Contents/MacOS/firefox -safe-mode
Once we started in Safe Mode window appears to us the following:
We have two options: