"Webpage is using significant memory. Closing it may improve the responsiveness of your Mac."

I get the following message quite often:

This webpage is using significant memory. Closing it may improve the responsiveness of your Mac.

My Mac is slow and the little wheel is constantly spinning. I have run disk checks, first aid, etc., it always says my Mac is good. I'm frustrated and open to suggestions.

Thanks,

Marion

[Re-Titled by Moderator]