Well, anything is POSSIBLE.
But:
I live alone, have no liberal friends, don't even speak to my liberal relatives, and anyone getting to this computer would have to get through my security system and edit my security videos, so it would have to be a 'professional' to get physical access to it.
And sure, a hacker could get in when I'm online, but that seems a silly game to play.
Then you’re probably encountering a ‘quirk’ of some kind with the browser. Perhaps something you’ve setup, like a folder you’re placing the bookmarks into, and not seeing them right away.
Try going into ‘Organize Bookmarks’ and search for them. They are probably in there somewhere.