Error log relating to history and high CPU on some Wikipedia pages

[Seb35]

Context:

• Firefox Nightly (149.0a1 (2026-01-23))
• in a private window
• only the extension ClearURLs activated (1.27.3)

When I open the page (1) https://fr.wikipedia.org/wiki/LCEN?useskin=vector it is correctly opened and redirected to (2) https://fr.wikipedia.org/w/index.php?title=Loi_pour_la_confiance_dans_l%27%C3%A9conomie_num%C3%A9rique&useskin=vector but there are side effects:

1. if I see during this opening in another tab about:processes the process Extensions uses 100% CPU during 3-4 seconds
2. if I open the DevTools of the tab, the console has an error Too many calls to Location or History APIs within a short timeframe. and a reference to the code sandbox eval code:1:9

Conditions where this issue appears:

• This is caused by ClearURLs because the side effects disappear when I disable ClearURLs and I reopen the page (1).
• Also, there is no issue with ClearURLs activated when the page (2) is opened directly.
• It occurs on all redirected articles when there is an additional parameter: e.g. https://fr.wikipedia.org/w/index.php?title=TFUE&useskin=vector has the issue but https://fr.wikipedia.org/w/index.php?title=TFUE does not have the issue
• When I disable "Prevent tracking injection over history API" in ClearURLs’ preferences there is no issue

This is probably a bad interaction with MediaWiki (the Wikipedia’s software) on redirected articles, since it does itself an history change with the history API (see here).

The error Too many calls… is probably triggered by Firefox when there are too many changes in the history API in a short time. But if there are other extensions doing some stuff for instance on the event tabs.onUpdated (called after the history API), then it could take longer and Firefox might not detect the issue and in this case the CPU remains at a high load indefinitely. It is in fact the original observation I did, but the root cause is what is described here.

[Seb35]

I searched in the other opened issues here, I guess these other issues are more or less related:

• Prevent tracking injection over history API: = (equals sign) at the tail of URLs when anchors are clicked #198
• On Brave, v1.23 causes 100% browser CPU on some sites #185
• CleanURLs breaks the History API #311

[Seb35]

Despite this reported issue, thanks a lot for this extension contributing to a better privacy !

I disabled the preference "Prevent tracking injection over history API" as a workaround.