Nano adblocker causes CPU spike under certain conditions

[liamengland1]

Describe the issue (Required)

Nano adblocker causes Chrome devtools to lag and eat CPU under certain conditions.

Screenshots (Required)

Screenshot of console (Required, press F12 to open the console)

It's empty

URLs where this issue occurs (Required if applicable)

http://example.com

Reproduction Steps (Optional if trivial)

1. Add example.com##* to my filters
2. Visit http://example.com
3. Open devtools

Anything else you believe to be useful (Optional)

Nano Adblocker adds display: none!important as an inline style over and over on the html tag on any site where a filter of type example.com##* is applied.

Cannot reproduce CPU spike in uBo or Nano firefox.

Environment (Required)

• Operating System and Version: Windows 10 1909
• Browser and Version: Chrome 83.0.4103.116
• Nano Adblocker Version: 1.0.0.149
• Nano Defender Version (Optional if you are not using it):

Your filter lists (Required)

N/A

Your custom filters (Required if you have any)

N/A

Your other extensions (Required if you have any)

N/A

[jspenguin2017]

Hum... Looks like a bug with the pseudo UserCSS engine.

@gorhill are you still maintaining the pseudo UserCSS engine?

[gorhill]

Frankly I think it's probably best to just drop pseudo user styles and fall back on using insertCSS() without the cssOrigin parameter, it's not worth maintaining a not trivial code base which is meant for pre-Chromium 66. The only consequence is that whoever uses old versions of Chromium may not have their cosmetic filters being enforced.

[gorhill]

Trivially fixed with gorhill@a5ba668.

Though I will still drop support of the pseudo version in next release.

[jspenguin2017]

https://bugs.chromium.org/p/chromium/issues/detail?id=1101473