I find Tumblr faster, Pinterest slower. Twitter mostly the same, but it’s often not loading at all. I had a wicked lag sometimes typing and that’s MOSTLY cleared up, but I’m getting lag scrolling from time to time. Haven’t recognized a pattern in sites or situations yet.
I did start checking out alternatives. Although my research might end up in the “open-forever tab graveyard” thing I got going on.
I used an old IE I had on the machine.
Youtube worked, so it ain’t the video card.
The new Fox is a pain.
I had this symptom a long time ago, and it turned out to be due to bad video decoding acceleration. My video card just couldn’t handle it, and I had to turn it off.
And, what do you know. The Firefox 57 notes include the following: “AMD VP9 hardware video decoder support for improved video playback with lower power consumption”
My guess is that VP9 acceleration doesn’t work properly on your graphics card. If it did, it would be an improvement. But, since it doesn’t, it actually makes other browsers that don’t use it look better.
Luckily. I was able to find a work around, as I expected:
If you were satisfied with how things worked before, then just go to about:config. Click through the warning, and then search and “media.wmf.amd.vp9.enabled.” Set that to false, and then restart Firefox. If I’m right about what the problem is, that should fix it.
(optional) If you would like better video acceleration, you can also turn of vp9 on YouTube. Do note this will limit your YouTube videos to 1080p max. That solution is to install the addon h264ify. I have this running on Chrome, and YouTube video is a whole lot smoother than it used to be.
It’s possible that, even if #1 doesn’t fix your problem, #2 still will. This would still mean VP9 is the problem, but it’s not something with the AMD driver. I would consider seeing if there is a newer version of the driver for your graphics card, and making sure you have all the updates for Windows 10, if applicable.
Heck, it wouldn’t hurt to check for graphics drivers even if the first fix works.
BTW, if the fix works, and you have the latest drivers and all the Windows updates for your machine, it would be good to report this as a bug to Firefox.
Also, another about config option I found while googling: “media.windows-media-foundation.use-nv12-format.” Set it to false. Though this problem is generally caused by having old graphics drivers–on Windows 8.
What does this mean?
“about:config”?
I don’t understand.
In the address bar where you would type a url such as “boards.straightdope.com” instead type “about:config” (no quotes) and hit Enter.
And the SDMB DOES IT AGAIN!!!
Woo-hoo!
Many thanks, BigT! 
So which part specifically helped?
Part 1!
Cool! That means I solved it on my own intuition rather than because I looked anything up.
May I suggest reporting this and the solution to Bugzilla? That way they have a chance to fix this so it doesn’t become a problem for anyone else.
They may ask you to set media.wmf.amd.vp9.enabled back to true and set media.windows-media-foundation.use-nv12-format to false, to see if that also works. If it does, that would be the better choice.
I didn’t want to start a whole new thread when we were all so successfully complaining about quantum here, so here is a question I have.
Other sites, including non-sdmb vbulletin sites, have tweet/instagram/etc embedding. I can’t see them any more. I lost it when quantum rolled out but I “fixed” it then with some tracker setting. All of a sudden last week I just see the words “Embedded tweet” or similar instead of the embedded tweet/other social media.
I can see the content on my other browsers and on mobile. I can’t see the content with my add-ons disabled. My trackers are set to whatever it is that lets it work (I also hadn’t changed them and I toggled them and checked for shit and giggles anyway, unsuccessfully). I checked some about:config csp setting that other people had trouble with.
I’m going out of my mind. I’m finding very little help through my google searches, and the other people with that problem fixed it via methods that aren’t working for me.
Anyone else encounter this? Or know how to fix it? It’s not deal-breaking, but it’s super inconvenient and I know it’s not my fault because it worked FINE before quantum.