he/she seems to be asking how to change the date format in firefox, not his tablet.
firefox usest US date format regardless of system settings which sucks.
eg. bookmark backups are date formatted YYYY-MM-DD and bookmarks 'added' date are MM/DD/YYYY and my, his systems are DD.MM.YYYY.
Firefox refuses to conform to the system's date format.
That's what argusmac was, is asking.
p.s., there is a preference setting for Thunderbird, but doesn't work in firefox. http://kb.mozillazine.org/Date_display_format
some say they've gotten it to work by setting prefs in about:config) (local and languages to en_GB instead of 'default' en_US (sometimes en-GB), but it hasn't worked for me in the most important way, the naming of bookmark backup files. From what I can find, Firefox will Only use the UTC date YYYY-MM-DD. I've installed nightly GB and RU versions and the date format for bm backups for instance remain ISO/UTC... sucks.
there is an addon that will add time / date to addonbar (bottom bar) that you can format date as you like [ https://addons.mozilla.org/en-US/firefox/addon/statusbardate/ ]