Safari 8.0.8 responding very slowly. problem started since Yosemite 10.10.4 update.

Update your OS X software to v10.10.5 then try Safari.

Open the App Store then select Updates from the menu.

Your Mac may restart several times on it's own during the update process. That's normal.

If updating does not solve Safari issue, troubleshoot Safari extensions and third part plug-ins.

From the Safari menu bar click Safari > Preferences then select the Extensions tab. Turn that OFF, quit and relaunch Safari to test. If that helped, turn one extension on then quit and relaunch Safari to test until you find the incompatible extension then click uninstall.

If it's not an extensions issue, try troubleshooting third party plug-ins.

Back to Safari > Preferences. This time select the Security tab. Deselect: Allow all other plug-ins. Quit and relaunch Safari to test.

If that made a difference, instructions for troubleshooting plugins here.

I either end up having to force quit or use another browser

Safari/Preferences/Advanced - enable the Develop menu, then go there and Empty Caches. Quit/reopen Safari and test. Then try Safari/History/Show History and delete all history items. Quit/reopen Safari and test. You can also try try Safari/Clear History and Web Site Data. The down side is it clears all cookies.Doing this may cause some sites to no longer recognize your computer as one that has visited the web site. Go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J. When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder. Select Library./Caches/com.apple.Safari/Caches.db and move it to the trash.

Safari Corruption See post by Linc Davis

From the Safari menu bar, select

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

and confirm. Test.