Set up extensions for a single browser variant

[xsmile]

Chromium doesn't utilize the External Extensions directory in Windows and won't read JSON preferences files. Currently extensions are set up as pre-installed but they are loaded by all Chromium variants of an OS user, assuming the registry entries are stored under HKEY_CURRENT_USER.

Find a way to workaround this limitation to allow extensions to be set up independently for each browser variant, possibly by patching Chromium.