I am not sure what is going on with my Macbook Air but it has been sloeing down to a crawl recently. I have Sierra or 10.12.6 and a mid 2012 iMac 1.7Ghsz i5). Ive never had this issue before but for the last twod ays this has been happening. I thought it was Opera at first because I have a lot of tabs open but it so,etimes does it on safari as well with almost no tabs running. I am thinking it could be steam or steam helper or I have some type of malware virus. The weird thing is this occurs after I browse for about 10 minutes: