Canvasblocker: Persistent high CPU load on some web sites

[ms1121]

While the tab is selected, I am seeing high CPU usage in Firefox on some web sites… as if a thread is remaining active and the process never completes. When I disable CanvasBlocker in about:addons and select the tab again, Firefox CPU loading for the page has returned to its normal idle state.

Example: https://homebiogas.com/

[kkapsner]

How many notifications do you see in the notification popup?

[kkapsner]

Can you please try the latest Alpha (you have to disable the normal first): https://github.com/kkapsner/CanvasBlocker/releases/tag/0.5.4-Alpha3

[kkapsner]

Please check https://github.com/kkapsner/CanvasBlocker/releases/tag/0.5.4-Alpha4

[kkapsner]

Please try 0.5.4: https://github.com/kkapsner/CanvasBlocker/releases/tag/0.5.4

[tavyra]

I'm on 0.5.4 and the problem still exists. Here's an address that will produce the problem without fail: https://www.windowscentral.com/how-use-custom-environments-windows-mixed-reality

[kkapsner]

Well... this pages requests ~200 DOMRect values per second - it seems that it's the ads. If I simply activate µBlock the number of requested DOMRects and therefore the CPU loads goes down.

As CB fakes this value I'm not surprised that you see an CPU load increase. But there is little I can do about it. I already try to be as efficient as possible.

PS: you will not see the high DOMRect numbers as CB only reports once for requests for the same object.

[kkapsner]

Can you please check which protection causes the problems on the other pages?

[tavyra]

I use ublock origin and umatrix, is there a rule or something I should add to keep this from happening? Disabling CB makes my cpu idle normally but I've only got like 70 notifications from ublock+umatrix+disconnect combined. I'm not sure what the other pages were that ended up freezing firefox and I can't think of any other add-ons that would be interfering.

Not knocking your efficiency either, with the exception of the random page that goes from 5% to 100% like a supercar, I haven't noticed any performance impact.

[kkapsner]

I do not know of a specific rule. I also use NoScript which also helps.

With number of notifications I mean the number in the page action popup (see screenshot in first comment).

[mitomenai]

I'm seeing some pretty bad performance dips on Amazon as of late. Browsing to a product and scrolling is extremely choppy, even after comments load. Issue seems to be stemming from DOMRect API.

Meanwhile, Audio API causes https://amiunique.org/fp to completely lock up.

[kkapsner]

Can you give an example link for amazon? It runs well for me.

The amiunique thing is known and there is not really anything I can do about it - they use a very poorly written script.
You can disable the audio cache temporarily to let it run a little bit faster. But I can tell you that it will say that you are unique...
If you want to test if the fingerprint is changing with every load you can use the CB test pages: https://canvasblocker.kkapsner.de/test/

[mitomenai]

Here's a random link:
https://www.amazon.com/Ultraviolet-Sanitizer-Sanitizing-Portable-Bacteria/dp/B007DK8FKW/

Keep scrolling, and once you hit the reviews it turns into a slideshow. Turning off DOMRect immediately resolves the issue.

I disabled all other addons, and the issue is still exhibited.

[spodermenpls]

@Leeweez I can't reproduce this issue either.. maybe open a new Issue, to share detailed information about your configurations and console logs?

[kkapsner]

Same for me. Page scrolls fine.

[kokoko3k]

For me, it slows down on amazon when the mouse is on the image product and the zoomed version appears to the right.
--EDIT--
You may need to search i also tried to disable the protection for dom api, but it is still slow.
the only way to make it fast seems to disable the extension.

[kkapsner]

What do you see in the page action popup:

[kokoko3k]

Sorry for the delay, i see the following:
Faked DOMRect readout on www.amazon.it (157)

[kkapsner]

Can you please give me your settings?

[kokoko3k]

Here they are (i've whitelisted amazon)

{
    "logLevel": 1,
    "urlSettings": [
        {
            "url": "www.amazon.it",
            "blockMode": "allowEverything"
        }
    ],
    "hiddenSettings": {},
    "expandStatus": {
        "blockMode": true
    },
    "displayHiddenSettings": false,
    "whiteList": "",
    "sessionWhiteList": "",
    "blackList": "",
    "blockMode": "fakeReadout",
    "minFakeSize": 1,
    "maxFakeSize": 0,
    "rng": "nonPersistent",
    "protectedAPIFeatures": {},
    "useCanvasCache": true,
    "ignoreFrequentColors": 0,
    "minColors": 0,
    "fakeAlphaChannel": false,
    "persistentRndStorage": "",
    "persistentIncognitoRndStorage": "",
    "storePersistentRnd": false,
    "persistentRndClearIntervalValue": 0,
    "persistentRndClearIntervalUnit": "days",
    "lastPersistentRndClearing": 1541763252068,
    "askOnlyOnce": "individual",
    "askDenyMode": "block",
    "showCanvasWhileAsking": true,
    "showNotifications": true,
    "highlightPageAction": "none",
    "highlightBrowserAction": "color",
    "displayBadge": true,
    "storeNotificationData": false,
    "storeImageForInspection": false,
    "ignoreList": "",
    "ignoredAPIs": {},
    "showCallingFile": false,
    "showCompleteCallingStack": false,
    "enableStackList": false,
    "stackList": "",
    "protectAudio": true,
    "audioFakeRate": "100",
    "audioNoiseLevel": "minimal",
    "useAudioCache": true,
    "audioUseFixedIndices": true,
    "audioFixedIndices": "11",
    "historyLengthThreshold": 2,
    "protectWindow": false,
    "protectDOMRect": true,
    "domRectIntegerFactor": 4,
    "blockDataURLs": true,
    "displayAdvancedSettings": false,
    "displayDescriptions": false,
    "theme": "default",
    "dontShowOptionsOnUpdate": false,
    "isStillDefault": false,
    "storageVersion": 0.4
}

[kkapsner]

Hm... I do not see anything bad there. Does the problem persist when you disable the DOMRect protection?

[kokoko3k]

Hi,
if i disable DOMRect API protection, the problem goes away.

[kkapsner]

Hm... I still cannot reproduce but I recommend that you then only disable the DOMRect API for amazon and not whitelist it completely.

[kokoko3k]

Thanks, but it is not clear to me how to disable just the DOMRect API for a specific site.
In the specific site option, i've "block only blacklist", but i'm unable to find where to edit this blacklist, or maybe i'm completely wrong and there's another way (?)

-EDIT-
Whops, sorry, i completely missed the checkbox :)

[kkapsner]

For all other searchers:

[Lucapz]

Someone on a forum had an old Windows XP box that he had to disable CanvasBlocker on as it caused websites like Amazon to become choppy like others have mentioned and he all so had to disable it on a more modern Linux skylake box as 60fps media at Youtube would stutter but was perfectly fine when CanvasBlocker was disabled so something is causing a high overhead or I/O polling that it's not always practical to use?

It might be something to do with Firefoxes API as other extensions can become sluggish on certain pages as i've noticed this with lastpass taking forever.

[kkapsner]

I always recommend to identify the part of CB that causes the slowdown (in the case of Youtube I would guess it's the DOMRect-API). The problematic parts can be disabled individually (also on a site by site level).

[lazycrypt]

I'm getting Firefox errors CanvasBlocker is slowing things down on https://steamdb.info.

This is what CanvasBlocker reports after the page loads (for instance, on the Sales page):

Faked DOMRect readout on steamdb.info
(92)

[kkapsner]

It's working fine for me - what are your settings and versions (Firefox/CB)?

[lazycrypt]

Other than appearance settings I'm running on the default CB settings. Testing it a bit more over the past two days the warning seems to appear only sometimes now. It could be that the official SteamDB Firefox addon could be conflicting with something, I'll test it out some more.

[codejodler]

Hello Korbinian,
I also noted excessive load after installing the CanvasBlocker addon/extension. Then i tried to figure things and found that another extension, EclipsedMoon (for the Palemoon browser) has a setting 'canvas.poison' checked, in the prefs section 'reduce fingerprinting', and when i uncheck that, the abnormal load is gone, at least on the few sites i tried since then.
This is not totally obvious since that Moon extension is supposed to fake useragents, but actually does a lot more.
So my idea is that the two are somehow fighting over the final result :D

I would not go so far as to notify the Eclipsed Moon developers. I mean, they're doing the best they can.
I think CanvasBlocker should just include a comment directly in the prefs, that the user is responsible for having not any other plugin mingling into the Canvas business.
Cheers,
mi

[kkapsner]

Hm... I'm not quite sure where to put such a comment so it's not too in the way but the people read it.

[spodermenpls]

@kkapsner Maybe put such a disclaimer just in the descriptions here and on AMO for now?

[kkapsner]

Sounds like a good idea.

[kkapsner]

Done

[mutantsushi]

This is website that triggers persistent script/CPU warning:
https://paizo.com/community/forums/pathfinder/playtest

Also, it happens on Twitter.

The warning doesn't occur, but Disqus discussions won't even display without CB disabled.
(not even logged in to be able to comment, but Disqus comments won't even load with CB)

[kkapsner]

I don't get a single CanvasBlocker notification or warning on this page. Please check the notifications to get to know which API/scripts trigger the CB protection.

Twitter is probably the DOM-Rect API. It usually gets a little bit better if you disable the notifications for DOM-Rect.

I have no clue about the Disqus problem (but I know that their technological approach is horrible). Can you give me an example page?

[AeliusSaionji]

I've just installed this extension today and can attest to it causing serious performance issues.

Observe: https://aelius.keybase.pub/canvasblocker%20amazon%20image%20performance.mp4

[AeliusSaionji]

Also, even when I'm not interacting with the Amazon webpage, firefox is chewing through 20% of my CPU when canvas blocker is loaded. Disabling canvasblocker and refreshing the page allows firefox to idle again.

(I've since read through the thread and excluded amazon from DOM-Rect api, which does sidestep the issue)

[kkapsner]

I am aware of this issue but have no good idea how to solve it. There is no good way to distinguish between fingerprinting and legit use of the DOMRect-API.

Maybe I should analyse the amazon code to get the exact problem...

[kkapsner]

The code at amazon is not great. It seems to me that they read the DOMRect more often than necessary. The numbers I get when I count every readout are insane (several thousand for one mouse movement). So the only thing I can do is to improve the overall performance of the DOMRect API.

[kkapsner]

I managed to get some performance improvements. The zoomed view at amazon is better but far of being good.

[kokoko3k]

Thanks kkapsner!

I'm thinking...
Would it be possible to add an "antihammer" option so that CanvasBlocker wouldn't allow more than (insert number here) requests per second?

[manyplay]

Hi,thx for the great addon!
Can you check the message system on ebay!
I have to disable the addon if i want to write a message...
The edit field is not writable...

[kkapsner]

@kokoko3k I could implement that but it would not help the user of such sites as it would completely break them. And despite it being written poorly it's a legitimate use of the API.

@manyplay please open a separate issue for your problem with all the details needed.

[kkapsner]

With the latest improvements the amazon page is usable. Not good, but usable.

[kkapsner]

Please test the latest 0.5.9 as it has some performance improvements.

[kokoko3k]

Definitely better, thank you!

[kkapsner]

I think with 0.5.10 the performance is acceptable. So I will close this issue. If someone still has an example page that uses lots of CPU or is slow I can reopen this issue.