Why dose flash player slow firefox down till its unuseable windows 7

Hi I'm running windows 7 every time i use flash based chat rooms they slow down and becomes totally unusable and youtube is very laggy too. I'm running Firefox version 24 (at the mo an upgrade from version 20 as the news the firefox the worse that seems to get) flash player version 10.3.18.48 (As 11 and upwards seems to get worse too) Ive tried quite a few of the suggestions in the about:config settings. Disabling hardware acceleration in flash player in the flash player settings and cleared any stored data. Ive put the MOZ_DISABLE_OOP_PLUGINS set that to 1 in the computer environment. Disable protection mode in the flash player. Made a new profile. changed the network settings in firefox auto detect proxy settings etc. Disabled my firewall to see if that made a difference, nothing. Ive disable the internet protocol versionv6 in the adapter local are LAN settings that done nothing too. the only plugin/addon i have if flash player Ive also ran Malwarebytes malware scanner, Kaspersky anti root, just to be sure and nothing came back. Ive tried opera but it wont run and wants me to update to flash player 11 tried Google chrome but that was useless it wouldn't even load the setting page and all i got was unresponsive page errors. Ive tried a few firefox tweeks up dated firefox downgraded firefox same problems continue. same problems were happening when i was using Windows Xp Sp1 and 2 so i upgraded to windows 7. The windows 7 I'm currently using is a fresh install ran out of things to try can anyone help please? Thank's :)