Is it true that if I tweet to @user1 and @user2 then this tweet is public?
But if I go to @user1's profile page and click "Tweet" to the user, then it is a private tweet?
No, Twitter doesn't have private tweets in that sense. (See below for an explanation.)
What if I go to @user1's profile page and then tweet to him but add @user2 to the tweet?
I found this worked for me.
Open the Firefox menu and head to Preferences. Then, under General settings head to Performance. Uncheck Use recommended performance settings and close the browser.
After start-up Twitter gifs played automatically.
Per Twitter's Help Center:
You will not receive notifications from accounts you block
However, there are some reasons why blocked accounts may show up in your notifications:
Tweets from others you follow that mention accounts you have blocked.
Tweets that mention you, along with an account you have blocked.
If you've already checked to be ...