Your block list is stored in a SQLite database. Here's how you can extract it.
(1) Open an online SQLite database viewer such as: https://inloop.github.io/sqlite-viewer/Keep this tab open because we are going to drag and drop a file onto it
(2) Open your currently active Firefox profile folder. This article has the steps: https://support.mozilla.org/kb/profiles-where-firefox-stores-user-dataSize this window so you can see the SQLite site behind it
(3) Double-click into the gm_scripts
folder, then scroll down to the Google_Hit_Hider_by_Domain_(Search_Filter_Block_Sites).db
file (sometimes the .db extension is not visible, but it will have a different icon from the folder of a similar name)
(4) Drag the database file onto the SQLite viewer page and it should immediately extract five data fields. The one you want is hideyhosts
-- you can paste it into the Import panel of GHHbD running in Tampermonkey or Violentmonkey.