Firefox slow on new Windows install/Flash player crashes, how to fix?

Question

On my new windows install I found Firefox to be very slow compared to how it was before the my new Windows install.
Opening most webpages takes way longer than it should, i excluded my internet connection being the problem as i always get 100/100 Mbps (speedtest) results.
I already :
-reinstalled Flashplayer, wich didnt solve the problem.
-Did a Firefox refresh (as in: https://support.mozilla.org/en-US/kb/firefox-health-report-says-your-browser-is-slow )
-Tried setting the ipv6 boolean (network.dns.disableIPv6) in about:config to true.
-Disabling plugins (user installed ones)
-Clearing flashplayer cache
-Reinstall videocard driver
I'm at a loss what could possibly be the problem, hopefully someone else has an idea how to solve this problem.
Thanks in advance

Answer 1

Do you ever see messages that scripts are running slowly with Stop/Continue options?
Another common troubleshooting step for Flash on Windows Vista and newer is to disable the plugin's protected mode feature. That feature has security benefits, but seems to have compatibility issues on some systems. There is a new hidden setting for this:
(A) In a new tab, type or paste '''about:config''' in the address bar and press Enter. Click the button promising to be careful.
(B) In the search box above the list, type or paste '''flash''' and pause while the list is filtered
(C) Double-click the '''dom.ipc.plugins.flash.disable-protected-mode''' preference to switch its value from false to true.
This might not take effect until all Flash has been unloaded for a few minutes, or you close Firefox.
Before that preference was added, the way to disable protected mode was by creating or editing a settings file. The following pages/posts provide different approaches for that if it turns out to be necessary (if Flash EXE processes continue to show up in the Windows Task Manager, Processes tab, even after changing the Firefox preference):
* Adobe support article under the heading "Last Resort": [http://forums.adobe.com/message/4468493#TemporaryWorkaround Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?]
* Manual steps: https://support.mozilla.org/questions/968190?page=5#answer-509209
* Batch file to automate the manual steps: https://support.mozilla.org/questions/982093#answer-518078 (alternate version of Carm's batch file with a few changes by me: [https://onedrive.live.com/?cid=f7d304d92388737d&id=F7D304D92388737D!336&ithint=file,.bat&authkey=!AP2FXW2Y_3BXZyo])
Flash needs to completely unload from memory (exiting and starting Firefox up again might help) before this takes effect.
Any improvement?