1. Go to this Adobe Flash Player Help page.
  2. Right-click on the Flash Player logo on that page.
  3. Click on Settings in the context menu. The Adobe Flash Player Settings screen will open.
   4. Click on the icon at the bottom-left of the Adobe Flash Player Settings window to open the Display panel.
                  
   
  5. Remove the check mark from Enable hardware acceleration.
  6. Click Close to close the Adobe Flash Player Settings Window.
  7. Restart Firefox. 

Update: The below solution was only temporary. A day later Firefox started crashing again. I find it interesting on how the problem was temporarily resolved. Refreshing firefox seems to help too, but so far no long term answer that I've seen. Could my McAfee be causing an issue? Firefox will start freezing momentarily then the open windows go black. Usually, I use task manager to close Mozilla, then reopen by clicking the Firefox icon. Doing it this way will bring up the window restore option so the windows you had open will be automatically restored. Im on a freshly updated win 10 but it did this before the update aas well. Flash is up to date ect. I usually have 10-30 windows open at a time hut have had it happen with less open. My laptop is about 5 years old but has an Intel I7 processor and separate video card as well as the integrated card. FireFox keeps crashing ? Try this: On the Menu bar click, Tools, Add ons, extensions. Disable anything video related, except for Flash player. I had 2 add-ons, OpenH264 video codec and Widevine content decryption module. I didnt bother with disabling just one of them, I disabled both. After this, close firefox and reopen. This fixed the crashing for me. Looks like a compatibility issue or to many video add ons conflicting with each other. You may want to disable Hardware acceleration of Flash player if you still have problems. Mozilla was still crashing when I disabled acceleration, just not as often. Disable hardware acceleration. https://helpx.adobe.com/flash-player/kb/video-playback-issues.html#main_Solve_video_playback_issues To disable hardware acceleration in Flash Player: 1. Go to this Adobe Flash Player Help page. 2. Right-click on the Flash Player logo on that page. 3. Click on Settings in the context menu. The Adobe Flash Player Settings screen will open. 4. Click on the icon at the bottom-left of the Adobe Flash Player Settings window to open the Display panel. 5. Remove the check mark from Enable hardware acceleration. 6. Click Close to close the Adobe Flash Player Settings Window. 7. Restart Firefox. This Flash Player Help - Display Settings page has more information on Flash Player hardware acceleration, if you're interested. To disable Hardware Acceleration Answer Provided By Mark Schmidt ttps://support.mozilla.org/en-US/questions/1058867