Like in dev. browser tools (for example, firefox) on the profiling tab understand why the page slows down?

Development | Software Testing
There is a site.When scrolling the page in some places, the page slows down(drops FPS), also when interacting with some elements and in moments of some animations also slows down.And the larger the screen size, the more the FPS drops.In different browsers, the FPS feeds in different ways, for example, in chrome, the brakes are almost negligible, and in the mozilla it is very slow.About mobile browsers silent.

How to find and recognize why this is happening?
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In Chrome, everything is clearly defined - how many requests are sent, how many are waiting for a response from the server, how much content is being loaded.And already from here we dance and find out why the page slows down.

on January 13th, 2020 (10:14 pm)
Use firebug plugin for troubleshooting.

Try other browser (Chrome,Firefox, Edge, Safari) if situation is same. Or scan pc for example 

on January 14th, 2020 (9:57 pm)
Thanks, firebug is great.
on February 04th, 2020 (7:55 pm)
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