Hi there and welcome
Can you tell me please how your transferring the emails to folders? Are you dragging them to the folder? And how long is it taking?
Can you do the following please in Safari
From your Safari menu bar click Safari > Preferences then select the Advanced tab.
Select: Show Develop menu in menu bar
Now from the menu bar click Develop > then click Empty Caches
Then close Safari, open it and tell me if you still have the problem please.
You will then see it under Safari (when you click it) Clear History and website data
ok, I think you missed my last instructions as your using a version that words it different, which I explained. I will repeat again below
I can also do these steps for you, and have made a request via Additional Services. This is optional, and if you choose to do this, I can, with your permission, remote into your computer while you watch and do all these steps (and deal with any problems that arise during them) for you. Or if you do not choose to take this service, we can continue here. This is no problem at all. Just let me know please.
Can you go to www.google.com/chrome
Download and install Google Chrome and with this installed, open it and within Google Chrome, go to Yahoo and access it.
Tell me how it now functions in Google Chrome please.
ok, to be sure Roger that's its nothing on your computer, I advise you do the following.
Power off the mac
Then start the Mac and hold down the Command and R keys at startup.
Hold these keys until the Apple logo appears. After your computer finishes starting up, you should see a desktop with an OS X menu bar and an OS X Utilities window
choose Disk Utility from the Utilities window, or from the Installer menu if you're started from an installation disc.
Click the First Aid tab.
Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
Select your Startup Disk (usually named "Macintosh HD").
Click Repair. Disk Utility checks and repairs the disk.
Let this complete and when it has, tell me if you still have the problem please.
ok, remove the power to your internet modem and wait 5 minutes.
While waiting, power off the mac.
Connect the internet modem, wait 5 minutes, power on the Mac and tell me if the speed has increased please.
What is the make and model of the router?
Can you on the back of the router hold the reset button in for 10 seconds then release.
Wait 5 minutes, restart the computer and tell me if you still have the problem please