I think most likely what is happening is that Flash is crashing, taking down plugin-container.exe with it. Have you worked through the Flash crash article?

Adobe Flash plugin has crashed - Prevent it from happening again

everything is up to date.. i don't get the flash crash message. my browser freezes and then i get a message that plugin-container stopped. i have tried everything.

There is another use for plugin-container.exe in the latest versions of Firefox:

e10s

One of the headline changes in Firefox 48-49 is e10s, which separates the browser interface process from the page content process (content processes move into plugin-container.exe). The performance impact of this can vary a lot between systems: many users find it faster, some find it slower, for many it's neutral. Hopefully by the time all the kinks are worked out it will work smoothly for everyone.

Are you using e10s?

You can check whether you have this feature turned on as follows. Either:

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, check the row for "Multiprocess Windows" and see whether the number on the left side of the fraction is greater than zero. If so, you are using e10s.

If you are using e10s:

To help evaluate whether that feature is causing this problem, you could turn it off as follows:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste autos and pause while the list is filtered

(3) Double-click the browser.tabs.remote.autostart.2 preference to switch the value from true to false

Note: the exact name of the preference may vary, but it will start with browser.tabs.remote.autostart

At your next Firefox startup, it should run in the traditional way. Any difference?

so it says 0/1 (Disabled by add-ons)

oddly now it says 0/2..

is there ANY way to stop it or disable it completely? (i tried all the old post suggestions about environmental variable settings, changing things to false in about:config and every other post for disabling it but none of them work anymore, it keeps coming back and keeps crashing my firefox).

thanks for ANY help:)

0/1 means you have 1 window open and it is not using e10s. 0/2 means you have 2 windows open and neither of them is using e10s.

The problem has to be a plugin, or sometimes a firewall or other security software "kills" plugin-container.exe.

I don't know of any way to force Firefox to run plugins in firefox.exe rather than spinning them off into plugin-container.exe.

Since Firefox doesn't support MP4 decoding on Windows XP (the Windows Media Foundation was never released for XP), you might consider reducing your reliance on Flash using the trick in this thread (I haven't tried it myself):

http://www.msfn.org/board/topic/175591-enable-mp4-h264-aac-html5-video-in-firefox-on-windows-xp-without-flash/