There is no need to suppress suggests since apt will by default never install them:
ogra@styx:~$ apt-config dump |egrep -i "suggests|recommends"
APT::Install-Recommends "1";
APT::Install-Suggests "0";
ogra@styx:~$
Firefox is only a suggests so it should not even attempt to install it (unless you tweaked your system defaults):
ogra@styx:~$ apt show libreoffice 2>/dev/null|grep -i suggests
Suggests: cups-bsd, firefox | firefox-esr | thunderbird, ghostscript, gnupg, gpa, hunspell-dictionary, hyphen-hyphenation-patterns,
imagemagick | graphicsmagick-imagemagick-compat, libgl1, libreoffice-grammarcheck, libreoffice-help (= 25.2),
libreoffice-l10n (= 25.2), libreoffice-librelogo, libxrender1, myspell-dictionary, mythes-thesaurus,
openclipart-libreoffice, pstoedit, unixodbc, gstreamer1.0-plugins-base, gstreamer1.0-plugins-good, gstreamer1.0-plugins-ugly,
gstreamer1.0-plugins-bad, gstreamer1.0-libav, default-jre (>= 2:1.8) | java-runtime (>= 8) | java8-runtime | jre, libsane1,
libofficebean-java
ogra@styx:~$
Also looking at the package description with apt show libreoffice:
You can extend the functionality of LibreOffice by installing these packages:
[...]
* firefox-esr | thunderbird | firefox:
Mozilla profile with Certificates needed for XML Security...
So it even mentions it does not actually need it and that these are fully optional…
When you mention 66 dependencies above that is not helpful without showing us the actual list it prints (which I assume rubi was after when asking you to run the command)