I meant that most major distributions had KDE available for those who were bothered by the lack of thumbnails.

Only the GNOME/GTK file picker did not display thumbnails for a while, but this functionality has now been available in all file pickers for some time.

Not so much a fork, rather a hardened Firefox, like Librewolf and Arkenfox on desktop.

Mostly from search engines, especially Google. They also own Mozilla Corporation, a for-profit entity which reinvests all of its profits back into the Mozilla Foundation.