From FreeSoftware Mac User Group:
Portable Firefox is the popular Mozilla Firefox
web browser packaged so you can carry around with you on any portable device, USB thumb drive, iPod, portable hard drive, memory card, other portable device (also on your internal hard disk) as long as it has 57 MB of free space and use on any Mac OS X computer, taking your bookmarks, extensions, history, cookies, and saved passwords with you.
- Drag the "Portable Firefox OS X" folder to your portable device, USB thumb drive, iPod, portable hard drive, memory card, other portable device (also to your internal hard disk) as long as it has 57 MB of free space.
- Clicking "Portable Firefox" will open Firefox from your portable device, wait a while before Firefox start.
Using your data
You can copy your local Profile folder to Portable Firefox when "Copy local Profile" window ask you. So, if you wish to use your bookmarks, add-ons, history, personal data and preferences you already have on your system, just click "Copy" when prompt, and select the folder "/Users/username/Library/Applications Support/Firefox/Profiles/********.default/" or any other profile you have on your local disk.
Download Firefox in your language from http://www.mozilla.org
and copy it to: "Portable Firefox.app/Contents/Resources/" folder.
Post questions, tips, suggestions, clues, helps, bugs to our Portable Apps OS X support forum