Resolved Safari very slow, lots of CPU usage with few tabs (less than 7)

[Gwendolini]

Hello.

Today Safari is acting up a bit. It is the latest version according to the Updates in the App Store.

Whenever I open a new tab/window/website, it takes up ten to 30 seconds until the site is usable, meaning until I can click on something or scroll it down and so on.
I cleared the cache, I restarted Safari several times and tried it with one tab or two tabs and so on.
I am currently using six tabs, and upon loading this rather not so complex site (from a visual point of view), the CPU spiked to 12.5% when it was normally just idling around 3%, even with loads of tabs open.
The CPU usage gets lower eventually, once the page is fully loaded.

Some hours ago, three BBC News tabs made the CPU use up to 50% of itself.

Any remedies besides switching to other browsers?

 

[Taz Mangus]

Hello.

Today Safari is acting up a bit. It is the latest version according to the Updates in the App Store.

Whenever I open a new tab/window/website, it takes up ten to 30 seconds until the site is usable, meaning until I can click on something or scroll it down and so on.
I cleared the cache, I restarted Safari several times and tried it with one tab or two tabs and so on.
I am currently using six tabs, and upon loading this rather not so complex site (from a visual point of view), the CPU spiked to 12.5% when it was normally just idling around 3%, even with loads of tabs open.
The CPU usage gets lower eventually, once the page is fully loaded.

Some hours ago, three BBC News tabs made the CPU use up to 50% of itself.

Any remedies besides switching to other browsers?

Create a new user, reboot and login to the new user account. If you use Safari do you experience the same issues in the new user account?

 

[Gwendolini]

Create a new user, reboot and login to the new user account. If you use Safari do you experience the same issues in the new user account?

Restarted. No help.
Tried another, already existing user. Did help, no lag there.

Where to go from there?

 

[Gwendolini]

Found the problem.

It was Tampermonkey and one of its scripts, I used one to load more than 40 comments on MR Forums. I disabled Tampermonkey and all is well.

Though I find it confusing, since no updates to Safari or Tampermonkey were made since the slow down started, at least not publicly, if Apple pushes some updates below the user's radar.