Firefox Multiple Profiles : the easy way

1. Amend folder structure as so:

-FirefoxPortable
    -App
    -Data
        -default
            -plugins
            -profile
            -settings
        -dev
            -plugins
            -profile
            -settings
        -light
            -plugins
            -profile
            -settings
    -Other

2. Put bat file in PortableFirefox folder and run!

3. (optional) place "Parameters.txt" in each new folder with a single line of command line parameters to pass to Firefox (e.g. -no-remote for dev profile).

.bat

@echo off
cls

:: Set MYPATH to Bat file directory
set MYPATH=%~dp0

:: Set the file where you profile list will be stored
set TMPTXT=%TMP%\FFprofiles_tmp.txt
:: Make sure it doesn't exist
if exist "%TMPTXT%" del "%TMPTXT%"


:: Store list of folders in \Data to FFprofiles_tmp.txt
dir "%MYPATH%Data" /AD /B /ON /P > "%TMPTXT%"

:SELECT
echo Available profiles:
echo.

setlocal enabledelayedexpansion
set choices=0
set i=0
for /f "usebackq delims=" %%a in ("%TMPTXT%") do (
set /a i+=1
set choices=!choices!,!i!
echo 	!i! %%a
)
set choices=%choices%,

echo.

set /p profile=Select by number (0 to exit):
if %profile%==0 goto END
if "%choices%"=="!choices:,%profile%,=!" (
echo Incorrect selection
pause
cls
goto SELECT
)


:RUN
set i=0
for /f "usebackq delims=" %%a in ("%TMPTXT%") do (
set /a i+=1
if !i!==%profile% set profile=%%a
)
echo Opening "%profile%" profile...

:: Check if FirefoxPortable.ini exists in current folder and copies from Other\source if not
if not exist "%MYPATH%FirefoxPortable.ini" copy /-Y "%MYPATH%Other\Source\FirefoxPortable.ini" "%MYPATH%FirefoxPortable.ini"

:: Start afresh with temp file
del "%TMPTXT%"

set params=
if exist "%MYPATH%Data\%profile%\Parameters.txt" set /P params=<"%MYPATH%Data\%profile%\Parameters.txt"


for /f "usebackq delims=" %%a in ("%MYPATH%FirefoxPortable.ini") do (
	set line=%%a
		for /f "tokens=1* delims=\" %%g in ("%%a") do (
			if "%%g"=="ProfileDirectory=Data" set line=ProfileDirectory=Data\%profile%\profile
		)
		for /f "tokens=1* delims=\" %%g in ("%%a") do (
			if "%%g"=="SettingsDirectory=Data" set line=SettingsDirectory=Data\%profile%\settings
		)
		for /f "tokens=1* delims=\" %%g in ("%%a") do (
			if "%%g"=="PluginsDirectory=Data" set line=PluginsDirectory=Data\%profile%\plugins
		)
		for /f "tokens=1* delims==" %%g in ("%%a") do (
			if "%%g"=="AdditionalParameters" set line=AdditionalParameters=%params%
		)
	echo.!line!>>"%TMPTXT%"
)

copy /Y "%TMPTXT%" "%MYPATH%FirefoxPortable.ini"

START /B .\FirefoxPortable.exe

:END
del "%TMPTXT%"
exit /B

EDIT: If you change the folder names of your new profiles after first run against that profile firefoxportable won't find your extensions properly...
Deleting .\Data\*folder*\profile\compatibility.ini and .\Data\*folder*\profile\extensions.ini after changing folder name seems to sort this out.