Can someone please say me how i can deactivate the open singleplayer cause i want to play the old game storiline
Open FLMM go to tools then click restore backups
Deactivate the Discovery mod.
What they're trying to say is you can't play the SP storyline with Discovery activated.
Unless you install an unmodded Freelancer to another directory. Well, I'm unsure about an actual 'install' but copy-paste works.
EDIT:
By the way once I found a downloadable 4.84 what had the original campaign with nano-using NPC-s - it made me swet blood.
I've been playing that one. Taking on the Rheinland fleet is complete madness.
GANKS! SO MUCH GANK.
So yes, if you want to play Disco singleplayer, the easiest way would be to download 4.84. Beware of the Grind, it's a fair bit more pronounced since there is next to no way you'll be able to take your freighter with you.