You may have spent years, months, or mere days getting your Firefox just the way you like it, but when you use a computer at work, school, or at someone else's house, you're stuck with the way theirs is set up, or more often the defaults. Wish you could take your settings and accounts with you wherever you go? Read on.

Steps:

1)Download the latest version of Portable Firefox, as it's often abbreviated, from PortableApps.com.

2)Plug in your USB device. It needs to be recognized by Windows as a drive. Note the drive letter.

3)Install Portable Firefox to the drive letter that Windows assigned your device to.
Portable Firefox is designed to work with PortableApps.com's menu platform, but this is for convenience. The menu is not required for any of their apps to run.

4)To copy your local Firefox profile to your USB device:
Follow the instructions on this page to locate your profile. Open the folder which starts with a series of random characters and ends in Default, or your profile's name if you have more than one.
Run Portable Firefox once and answer the setup questions. (Always run FirefoxPortable.exe from the installation directory; NEVER run firefox.exe from the subfolders. This launcher ensures that Firefox runs correctly in a portable environment, and cleans up after itself when it is finished to ensure no personal information is left behind.) Now close Portable Firefox.
Open your USB device, and browse to the installation folder, then Data, then Profile.
Delete everything from the Profile folder on your USB device. Take care that you are clearing the right Profile folder.
Copy everything from the local profile folder to the Profile folder on your USB device.
Start FirefoxPortable.exe again to ensure that Firefox Portable is using your local profile.

5)To install Flash and Shockwave to Firefox Portable:
Browse to Adobe's Flash homepage and download and install Flash. You must have the regular version of Firefox installed to do this, but you only need to do it once.
Browse to Adobe's Shockwave homepage and download and install Shockwave. You must have the regular version of Firefox installed to do this, but you only need to do it once.
Browse to your local profile directory as outlined above. You're looking for a folder called plugins. If that search isn't fruitful, consult this MozillaZine article. If that isn't helpful either, search your Windows drive for NPSWF32.DLL. Open the folder it's stored in.
Open your Firefox Portable plugins folder, located in the Data folder.
Copy every file from the local plugins folder to the plugins folder on your USB device.