I always use "subst p: %CD% >nul 2>nul" to mount my portable drive.
This has given very good service over many years.
I am new to PortableApps and love Firefox/Thunderbird - specifically because Firefox takes it's full profile on the stick (unlike Chrome).
However, when I add extensions they disappear when I move to another computer and am allocated a differnet initial drive letter.
I can carry them *.xpi and "install from file" - every time - but it's a pain.
Is this a know limitation of adding extensions to Firefox/Thunderbird?
Is there a solution?
OS - Windows 10
Firefox - 77.0.1 (64-bit+32-bit)
Thunderbird - 68.9.0 (32-bit)
See more here
Do note, I believe it was fixed in the latest version of Firefox. Appears you have it, maybe someone else has a better response
Just thinking that maybe you are not using the supplied launchers.
For Firefox the launcher has the title FirefoxPortable.exe and that will be in the root folder of the folder you installed Firefox Portable to.
For Thunderbird the launcher has the title ThunderbirdPortable.exe and that will be in the root folder you installed Thunderbird Portable to.
It is essential that you always launch your PortableApps using the supplied launcher -- if you do otherwise then you compromise the portable aspect of the PortableApp. All programs supplied by PortableApps come with a launcher and they must be used.
Also I'm wondering where you got your Thunderbird (Portable?) version 68.9.0 from -- certainly not from PortableApps as that version hasn't been built nor released by PortableApps as yet. As it stands you should only update your PortableApps using the latest versions officially released by PortableApps -- don't update your ThunderbirdPortable from any other source as you risk messing it up if you do.
Use Portable Apps on both Flash Drive and HDD/SSD.