Edit: I found out that the add-on warns about high CPU usage for some of its presets (Preferences->General->Presets). Using a different preset has removed that ~10% CPU usage.
Some preliminary context: Since one or two updates ago, I’ve noticed that Firefox is using around 10% CPU even then all tabs are unloaded. This didn’t happen before. The add-ons I use are still the same, and I have blocked the new LLM functionality. (Maybe someone else noticed the same?) Anyway, in order to investigate, I’m switching off the add-ons one by one, as usually done, checking if the situation improves.
While doing so I was wondering whether I still need Canvas Blocker. I see its most recent reviews are 4 years old now. Does anyone know whether it’s still needed for privacy, or if Firefox now provides some of the same functionality built-in? I do use AdBlock Origin as well.
Thank you for info and opinions!
Closes Firefox. Opens with no tabs. looks at
top -d20for a few rounds each way. Repeats with Canvas Blocker disabled and Firefox restarted. Looks at the about:performance tab in Firefox, looking at Extensions CPU usage each way.On my system, it’s mostly in the neighborhood of 0.4% CPU usage while idling with no tabs either way. I don’t see any overwhelming difference. CPU might be a hair higher with that addon enabled, but I’m not willing to spend a lot of time taking a ton of samples looking for for very small differences. You could measure it on your system for an extended period of time if you wanted, though, hammer down exactly whether there’s any impact.
From my tests without it the id I was assigned from canvas tracking was repeatable. After enabling it the id was different every time. So to me it seems to be still needed
Now try with fingerprintingProtection (set overrides to +AllTargets) and resistFingerprinting in about:config
Huh. That got weird. I’m using Fennec, used https://whatdotheyknow.app/ for checking
With what you proposed the canvas id did keep changing (good) but browser fingerprint stopped changing. And disabling AdNauseam (uB with malice) didn’t change anything
Hmmm, that’s odd. Although mobile browsers are fucky in general, not much to do there. If you enable letterboxing, the UI will be ugly but you will be more likely to share fingerprints with someone else who enabled that specific feature… Which is a while lot of nobody. If you don’t enable it, but use a 720p phone with default font size, you might share a fingerprint with me, lol. Or just wait until home and use a desktop computer. Or Librewolf PostMarketOS…
OR can’t get fingerprinted if you embrace it. Get chawan. No site will be adapted to do stuff with that.
As for why there’s a difference between the extension and built-in stuff, no clue.
Great piece of info, thanks!
I removed it a year ago for this same reason. Love the extension, hate the seemingly unjustifiable CPU usage.
I found out that the add-on itself warns about CPU usage, depending on the settings. It has a preset with low CPU usage.
Walmart.com doesn’t like it, but otherwise I think it’s useful.






