If safari is slow some trouble shooting steps are there :
open safari > safari > safari preferences > security > enable java scripts & all options , remove if any extensions .
If any anti virus , third party software /app from the system is installed please uninstall it and its plist should also be removed from system library & user library .
Go to user library ( hidden library ) : click on go > hold option key & don't release it > library .
Remove the contents of following folders by selecting them , can use command + A , & delete them command + delete into trash .
Caches , cookies , application support , saved application state , logs , launch agents .
particularly in safari folder if the user is using bookmarks select all contents except bookmarks & delete them into trash.
restart from apple logo & empty the trash .
Don't get panic fresh new contents will be created once again .
Lastly you have to once again configure web mail , i cloud ( you must have four digit verification code ) , settings in system preferences .
also for spinning beach ball issue : execute safe mode & run SMC , PRAM .