A profile in firefox is method of grouping all your personal date, ie bookmarks, extensions, passwords as and so on, much like the user in windows, which is separate for each user having his preference, files etc.

So while moving from one version to another or simply for the sake of periodic backup a simple way to save all your firefox data would be to just save your profile folder and restore it back.

To find out the location of the profiles folder in your installation, open up firefox and then type the url as about:support and press enter.

Now find and click the option called “open containing folder”. Now you will be taken to the profile folder which you can then manually backup to a place of your choice. There are extension to do this like FEBE which can automatically do the same thing, but it might be worth while to know this tip too.