Hello Ruthenberga,
Thanks for reaching out to the Apple Support Communities. I understand you've had some trouble with popups when using the Facebook App, and I have some information that may help.
In cases like this, it may help to clear your website data by going to Settings > Safari > Clear History and Website Data.
If the issue persists, you can clear further data by going to Settings > Safari > Advanced > Website Data. There you can choose to clear all the website data or, you can tap edit to remove specific sites that may be causing the issue.
If the behavior persists or you run into any trouble, please reach out again.
Best Regards.