To whom it may concern...
I found that to run current versions of Firefox - also including ESR and SeaMonkey - the file pdh.dll is missing in \FirefoxPortable\App\Firefox. You will get the following error message: "XPCOM is missing"
As it looks you can use any 32bit pdh.dll as far back as Windows 6 (Vista) - works also on all newer WindowsPE versions including Windows 10 PE or Core.
If you have a 64bit Windows install copy pdh.dll from %windir%\SysWOW64\pdh.dll
Maybe recommended to the maintainer of this Portable App to include the DLL in future releases.