User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:51.0) Gecko/20100101 Firefox/51.0 Build ID: 20170125094131 Steps to reproduce: As usual, tried to measure my speed connection first using speedtest.net site, then its beta version beta.speedtest.net. Actual results: The speedtest.net Flash application properly measures the speed, but the visual rendering is broken - while the needle goes to the right, its pieces are left over, the number showing the instant speed is kinda half-covered. I tried beta.speedtest.net (it is HTML5-based version, no Flash used), everything works perfect. I have tried both 32-bit and 64-bit version of Firefox v51.0.1, same behavior. Windows 10 Pro N 64-bit is being used. OK, tried it again on my laptop w/Windows 10 Home SL/Firefox 51.0.1 32-bit. Flash version behaves exactly the same - instant speed counter broken, pieces of the needle on the screen. Beta version w/HTML5 works perfect.

Did you test with a fresh profile? https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles Did you test with multiprocess disabled?

OK, I tried first applying a fresh profile - no help. Disabling multiprocess - I set browser.tabs.remote.autostart.2 to false (browser.tabs.remote.autostart was set false by default). Same result as before.

Ok, I see. I'm able to reproduce the issue with FF50 on Win 7. But not with FF52 or FF54.

I admit this looks bad, but as just a visual glitch we're probably not going to dedicate engineering time to figuring this out. It possibly will be fixed by the new async drawing feature that we're working on with Adobe.

(In reply to Loic from comment #4) > Ok, I see. I'm able to reproduce the issue with FF50 on Win 7. But not with > FF52 or FF54. In my case FF50 did not have this problem on Windows 10 Pro N and Windows 10 Home SL.

FF53/54 dont have this issue, probably fixed.

Another example: http://www.jacquielawson.com/ecard/view?code=6694960224539&ob=1

Interestingly enough, this bug does not apply to Windows Server 2008 R2 Standard (Service Pack 1). FF51 passes the speedtest with flying colors.

Given comment 5 I'm marking this fix-optional for the currently-in-play releases.

Another example: https://support.mozilla.org/t5/image/serverpage/image-id/632i4F5CFEC821C3DD1D It affects SWF games, which is definitely more of a problem than just viewing a speedtest. Disabling hardware acceleration in Flash and Firefox solves the problem for some SWF objects, but not all. Speedtest.net is one that is always affected.

I run Windows 7 Pro 64-bit with Service Pack 1. I have Firefox 51.0.1. I have been seeing this too. I thought it was perhaps the fault of hardware acceleration so I tried turning that off both in the browser and for flash itself. It did not seem to do much. I noticed this issue on speedtest.net myself as well.

I confirm it's fixed with dom.ipc.plugins.asyncdrawing.enabled=true.

(In reply to Loic from comment #15) > I confirm it's fixed with dom.ipc.plugins.asyncdrawing.enabled=true. Yes, it sure did take care of it! Thanx

(In reply to Loic from comment #15) > I confirm it's fixed with dom.ipc.plugins.asyncdrawing.enabled=true. That works for me also. Now to push that fix out to the average user.

Async drawing has been disabled due to many various regressions, but it going to be enabled again in the next versions.

Working properly now on http://www.speedtest.net/

Also, confirming fixed for me on FF 52.0 (Win 7 Pro) on my jacquielawson card (http://www.jacquielawson.com/ecard/view?code=6694960224539&ob=1) with the change in setting dom.ipc.plugins.asyncdrawing.enabled=true Thanks to whoever figured that out :)