I just had Firefox, which always work OK, update to some new version. I have a 6th gen i7 quad core hyperthreaded laptop with 4gb video and on board video separate and 16 gb ram and it takes 4 seconds just to switch back between already opened tabs, and any activity because so slow as to be unusable. I couldn't even use Firefox to submit this issues. I don't use bitdefender or the other listed causes. I don't even use a lot of extensions. I'm on the latest windows 10 and the primary HDD is an SSD drive. IE 11 has no new performance problems, this is limited to Mozilla. Note that my internet connection is not fantastic, it's DSL 3 MB/s, not some blazing high speed internet, but Mozilla is maybe 10-50 times slower than IE11 on the same site or more in some cases, sometimes not even finishing rendering a page for minutes. Mozilla was about the same as IE before the latest update in performance on average. It was very usable and I used it :)