If "Please enter the master password for the Software Security Device" is driving you mad because you have to enter your master password several times whenever you launch Mozilla's free Firefox browser or Thunderbird email software, the easiest solution to the "too many master password boxes" problem (or annoyance!) is the following tip.
Simply install the StartupMaster add-on / extension for Firefox and, separately (if you use Thunderbird) also the StartupMaster extension for Thunderbird (if necessary see how to install a Thunderbird extension - you don't just click on the link unlike in Firefox).
Restart Firefox or Thunderbird (whichever you need to sort out), and thereafter you shouldn't have to enter your master password more than once for Firefox and once for Thunderbird.
Background - you may have to type the master password several times in Firefox or Thunderbird if you've set a master password (which is a good idea for security reasons) and you've also set Firefox's home page to open in tabs more than one web page with login for which you've stored passwords - or if you've set up Thunderbird for more than one email account.
You'll get one password box, which you have to fill in and OK, for each Firefox tab with saved password or each email account you've set up in Thunderbird.
You may also have to keep clicking Retry (after entering the password in every single popup box) if you didn't enter the master password very shortly after Thunderbird opened, eg you left the computer for a few minutes then came back to it.
In some earlier versions of Firefox you didn't have to tediously enter the same master password many times in this situation, but sadly you do now. Unless you get the add-on I suggested.