I have a file:/// url I access every day. That showed up in the new tab
tiles as expected. It's even pinned there.

Recently, that tile has gone missing from the page, a blank space is
where it should be. If I manually open the file:/// url, and then open a
new tab, the tile comes back, and remains in the new tab page until I
close firefox. Each time I close it, it forgets about this one tile again.

(In case it matters, the full url is
file:///usr/share/doc/ghc-doc/html/libraries/index.html )

src:iceweasel has been superseded by src:firefox-esr in version
45.0esr-1 in March 2016. Transitional packages to ease upgrades were
provided in the wheezy, jessie, stretch and buster releases. The
transitional packages have been removed finally before the bullseye
release in August 2021.
After regular security support for buster ended in August 2022 and LTS
support ended in June 2024, I'm closing the remaining bug reports now.

Andreas