Why do my webpages blink on and off

1. From the Safari menu bar, select

Safari ▹ Preferences... ▹ Extensions

Turn all extensions OFF and test. If the problem is resolved, turn extensions back ON and then disable them one or a few at a time until you find the culprit.

2. Select

Safari ▹ Preferences... ▹ Privacy ▹ Remove All Website Data...

and confirm. Test.

Poorly written web pages will cause that to occur. Generally, those websites are characterized by advertisements containing resource-hungry code.

If that behavior occurs on many websites, such as this one, write back for recommendations. Apple Support Communities is one of very few websites that do not inundate users with advertisements.