MutationObserver.observe (?) hanging in 12.6

[etomzak]

I'm seeing minutes-long hangs and timeouts on Firefox 138.0.1 with NoScript 12.6 on Linux. Downgrading to NoScript 12.1.1 appears to resolve the issue.

Using the Firefox built-in profiler, I can see that MutationObserver.observe is taking an inordinate amount of time in NoScript 12.6 (on the order of 90% of page load time on one particularly problematic HTML page).

I'm happy to try to debug this some more, but I'm not a Web guy, so I really have no idea what I'm looking for.

[hackademix]

Is your "problematic HTML page" a local (`file://' URL) one? Culd you please share it for testing?

Thanks!

[etomzak]

Is your "problematic HTML page" a local (`file://' URL) one?

Yes

Culd you please share it for testing?

The one I was looking at is confidential, unfortunately, but I've found a public one that exhibits the same behavior:

https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html

It's a fairly simple page, but very long.

I did some testing: When I load the page from the internet, then performance is as expected, but if I save a local copy and open that, performance goes to a crawl.

[flibbles]

I am also having this same issue. In 12.6, any attempt to load "file://" urls will hang for several seconds. Had to revert back to 12.1.1