User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:67.0) Gecko/20100101 Firefox/67.0

Steps to reproduce:

openSuse leap 15.0

i launch FF with "firefox --safe-mode" to make test
then
i close FF
then
i launch FF with "firefox"

Actual results:

i get a message "using an older version of firefox can corrupt bookmarks..." with buttons "quit" and "create a new profile"
then i quit
then
i launch "firefox -P" and choose "default"
then
i get again "using an older version of firefox can corrupt bookmarks..." with buttons "quit" and "create a new profile"
then
i launch FF with "MOZ_ALLOW_DOWNGRADE=1 firefox -P"
then
i get my default profile with my default settings
then
i close FF
then
i launch FF
no more problem

it's a known problem

https://techdows.com/2019/05/switch-to-old-profile-from-new-profile-in-firefox-67.html

https://www.reddit.com/r/firefox/comments/brjj82/firefox_67_thinks_its_an_old_version_and_wont/

https://www.askvg.com/fix-all-bookmarks-add-ons-and-settings-lost-in-mozilla-firefox/

if you read the links you'll see this is not a corruption problem of bookmark.

this is a problem with new profile per install architecture feature they introduced with Firefox 67.

see
https://bugzilla.mozilla.org/show_bug.cgi?id=1553526
https://techdows.com/2019/01/dedicated-profiles-per-installations-to-begin-with-firefox-67.html

Thanks for the report, we've already fixed the safe mode issue in bug 1556612. I believe 67.0.2 will soon be released which will fix this.