Sorry, the "manual Sync" button was removed from Firefox quite a few versions ago, when the "Sync Tabs" feature was added. The old "manual Sync" button was removed when the "Sync Tabs" button came about.

All you can do is to "Disconnect" from the Sync server and then Connect again when you want Sync active again. Royal pain in the a$$ now. That was a feature that I used often.

You can find a Sync button (two arrows in a circle) in the "3-bar" Firefox menu button drop-down list next to the Sync email address when you are connected, but Firefox will probably still sync automatically if you make changes that need to be synced.

cor-el сказал(а)

but Firefox will probably still sync automatically if you make changes that need to be synced.

Yes, thats the question! How to make ff sync only by button, without automatic updates