You need to uninstall both of them, and install the most recent version of Flash, 17. https://get.adobe.com/flashplayer/download/?installer=FP_17_for_Firefox_-_NPAPI&standalone=1

To try a few more things that could improve your performance:

• Troubleshoot Firefox issues caused by malware
• Refresh Firefox - reset add-ons and settings
• Upgrade your graphics drivers to use hardware acceleration and WebGL

ActiveX is for IE and possibly for some desktop applications that embed Flash.

This is some standard guidance that addresses the most common issues with the Flash Player plugin. It might partially duplicate the above, but just in case:

(1) If you have any recorders/downloaders that interact with Flash media make sure they are as up-to-date as possible, or disable them temporarily.

(2) Disable hardware acceleration in Firefox and in Flash

(A) In Firefox, un-check the box here:

"3-bar" menu button (or Tools menu) > Options > Advanced > General > "Use hardware acceleration when available"

That takes effect the next time you exit and start Firefox up again.

(B) In Flash, right-click the media and choose Settings, then the first mini-tab and uncheck the box to use hardware acceleration. More information in this support article from Adobe: http://helpx.adobe.com/flash-player/kb/video-playback-issues.html#main_Solve_video_playback_issues

(3) Disable protected mode (Windows Vista and higher)

The protected mode feature of the Flash player plugin has security benefits, but seems to have compatibility issues on some systems. There is a 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.

If Flash 17 cannot be made to behave well, there is an "Extended Support Release" version of Flash 13 available here: https://www.adobe.com/products/flashplayer/distribution3.html (scroll the page about halfway down, it's the one for plugin-based browsers). Most likely you would need to remove all Flash before trying to install that, or Adobe's installer will correctly claim you already have a newer version.

Thanks Tyler Downer and Jscher2000. I uninstalled Flash Player 16.8 and installed 17.x. That seems to have fixed the lag issue when scrolling and so far, the video issue as well. Thank you both for all the good info.