Canvasblocker: Prevents loading of websites and breaks JS

[rugk]

I just had an issue where Firefox would not execute JS on some pages (although no add-on blocks it or so) and when restarting and restoring the tabs I see that all of my pinned tabs will never load (even as one is in the LAN, so it is certainly not a network error). It also affects some other tabs when these are not directly loaded from the cache.

Firefox 57
Fedora 27

[AnttiBoman]

I can verify this problem. Some web pages stopped loading altogether or partly today on Firefox at home, and now also at work. I suspected it was because of some add-on, and disabling CanvasBlocker made everything work again.

If you need help spotting the problem, please let me know.

Keywords: Ubuntu 16.04, Firefox 57.0.1 (64-bit)

[kkapsner]

Can you please try version 0.4.3a?

Which additional addons are you using?

[rugk]

From the ones, which could also cause problems: Decentraleyes, Cookie AutoDelete, KeePassHttp-Connector, uBlock origin

[Biggizen]

Same here. Until today there was no problem, but now I have to disable CavasBlocker for some sites like startpage.com to make them able to load. The same sites loaded without problem before today. I did not make any changes in the settings of CanvasBlocker.
I also did not install any other add-ons today.

[rugk]

Quite mysteriously that it kicked off today, indeed…

[kkapsner]

I published a new release yesterday night - so not that mysteriously.

[kkapsner]

But the problem is weird: no problem for me (same as #160 - but I assume same source)

Any special settings for the addons? Or just the default ones?

Can you please disable all other addons and see if the problem still occurs? If not: in which combination does it?
Can you try on a fresh Firefox profile?

[rugk]

Just the default settings for CanvasBlocker. Tried it in a another profile – could not reproduce.

[kkapsner]

That's exactly my problem. I need a way to reproduce it to sole the problem efficiently.

[kkapsner]

Can you please create a copy of your affected profile and change the order of the webExtensions in extensions.webextensions.uuids?
Is CanvasBlocker in front or in the back or in the middle?

[kkapsner]

I created three beta versions. Please check if any (or all?) solve the problem:
https://github.com/kkapsner/CanvasBlocker/releases/tag/0.4.3-Beta.4
https://github.com/kkapsner/CanvasBlocker/releases/tag/0.4.3-Beta.5
https://github.com/kkapsner/CanvasBlocker/releases/tag/0.4.3-Beta.6

Also check if the problem is still present in
https://github.com/kkapsner/CanvasBlocker/releases/tag/0.4.3-Beta.3

PS: you should disable the normal version before installing the beta.

[AnttiBoman]

I'm not sure if it's a CanvasBlocker problem, after all. Disabling it worked at the work computer, but not at home.

[kkapsner]

I'm quite sure it's a problem with a combination of addons and some special circumstances. I just want to remove the CB part.

Have tried to completely uninstall CB, restart Firefox and reinstalling CB?

[rugk]

So tried a few things…

• I could disable all other addons and only leave CanvasBlocker enabled and the issue was still there
• disabling CanvasBlocker and restarting FF, the issue was gone
• in extensions.webextensions.uuids the add-on was somewhere in the middle, changed it to be at the beginning, nothing changed…
• I left FF running with that issue a while and did nothing else (just let these pinned tabs load until infinity…) and it caused a memory leak or so, in any case the "Web Content" process used 6GB RAM then…

[rugk]

AFter installing 0.4.3-Beta.6 the issue was gone, but when I tried to reproduce it with the other old version (disabled beta, re-enabled stable) it also was not e producible anymore.

Edit: Well… no, it just needed yet another restart.

[rugk]

So anyway: 0.4.3-Beta.6 fixes the issue. It also seems to be fixed with v0.4.3-Beta.3.

[kkapsner]

Thanks for the input. New release is out: https://github.com/kkapsner/CanvasBlocker/releases/tag/0.4.3c-Release
I guess it will be validated and shipped by Mozilla soon.

[kkapsner]

Can you please check if the problem is still solved in the version on the beta channel: https://addons.mozilla.org/de/firefox/addon/canvasblocker/versions/beta

[rugk]

Unfortunately I just updated and the issue is not solved with v0.4.3c. Also the 0.4.4alpha20171219 does not make it work.

Maybe it is more about the settings/data collected from the add-on. So I looked into it and saw, e.g. the "max. fake size" set to 0, huh? (I did not manually change that, just so you know.)
I reset the settings, so maybe that helps…

[rugk]

Hey nice, after resetting the settings (Note I created https://github.com/kkapsner/CanvasBlocker/issues/170 before) it works. So it is clearly some bogus setting…

Just FYI in the previous versions I also had a whitelist (domains). This was also not shown in my current version.

And note it still resets the "max fake size" to 0 (it's also present in the export "maxFakeSize": 0,). ANd when I reset the settings again and activate expert mode, it still shows me the setting as 0… Huh, there is clearly something wrong with these settings.

FYI here is the full export (it is supposed to be nearly the default, as I clicked on that button few times):

{
    "logLevel": 1,
    "urlSettings": [],
    "whiteList": "",
    "blackList": "",
    "blockMode": "fakeReadout",
    "minFakeSize": 1,
    "maxFakeSize": 0,
    "rng": "nonPersistent",
    "useCanvasCache": true,
    "ignoreFrequentColors": 0,
    "minColors": 0,
    "fakeAlphaChannel": false,
    "persistentRndStorage": "",
    "storePersistentRnd": false,
    "persistentRndClearIntervalValue": 0,
    "persistentRndClearIntervalUnit": "days",
    "lastPersistentRndClearing": 0,
    "askOnlyOnce": "individual",
    "askDenyMode": "block",
    "showNotifications": true,
    "storeImageForInspection": false,
    "notificationDisplayTime": 30,
    "ignoreList": "",
    "showCallingFile": false,
    "showCompleteCallingStack": false,
    "enableStackList": false,
    "stackList": "",
    "displayAdvancedSettings": false,
    "displayDescriptions": false,
    "isStillDefault": false,
    "storageVersion": 0.2
}

[rugk]

BTW this is what a test result looks like: https://screenshots.firefox.com/ZpFqVyuZFLVjxakG/browserleaks.com

[kkapsner]

Thanks for the effort. and This is great input! There was a settings version change between 0.4.2 and 0.4.3 and maybe the migration has the problem. Can you remember you settings before resetting? Something else than a whitelist entry?

PS: maxFakeSize of zero is OK. It means that any size will be faked (In the description it should mention that or is this not clear enough?)

[rugk]

(In the description it should mention that or is this not clear enough?)

Umm, no… 😐
It just mentions you should never set the value under 1000000 or so… And 0 is below that 😃 .

Basically I just once added two domains to the whitelist. This was long before the WebExtension migration though. AFAIK I've changed nothing else.

[kkapsner]

At the beginning it states "(Enter zero to disable.)" - should this be more prominent?

OK - then I will try the migration with two domains in the whitelist. Hopefully this reproduces the problem and I can work on the fix efficiently.

[kkapsner]

No luck... still not reproducible - this is so annoying.

[kkapsner]

Does the blocking come back when you add the whitelist entries again?

[kkapsner]

At least I found a minor bug in the migration...

[rugk]

At the beginning it states "(Enter zero to disable.)" - should this be more prominent?

I don't see that. Maybe the German translation is also outdated.

[kkapsner]

In German it says "Canvas, die eine größere Fläche als die hier angegebene Zahl haben, werden nicht vorgetäuscht. (Null eingeben, um es zu deaktivieren.) Dies ist ein Leistungsparameter, der das Einfrieren des Browsers verringern kann und der an die Rechenleistung des Gerätes angepasst sein soll.
ACHTUNG: Dies verringert die Sicherheit des Addons. Deswegen wird stark empfohlen, diesen Wert nicht unter 1 000 000 zu setzen.".

[kkapsner]

The latest alpha (https://addons.mozilla.org/de/firefox/addon/canvasblocker/versions/beta) fixes the issue. Indeed this is not an alpha any more and I will generate version 0.4.4 immediately - I guess it will be available in about 30 minutes.