How to tell if there is an error message page in firefox

https://support.mozilla.org/z.

A competitor"s site is embedded in iframe. I hope to do something when the "your connection is not secure" page" appears.
how can I tell if there is an "error message page"?

Https html javascript firefox
Apr.11,2021

js should be able to listen for events corresponding to iframe, or will there be a status code?
anyway, the general idea is to listen for the event and then execute the processing.

Previous: How to display the output of different processes in different areas of the same screen at the same time under the linux terminal?

Next: Robo 3t deleted mongodb collection Times error

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1be0a27-31517.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1be0a27-31517.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?