Add-on laggy in Firefox

My Firefox started to become laggy regularly, and today I figured I’d investigate. In `about:processes, I’d see the “Extensions” process taking up lots of CPU time (up to 90%), and then disabling the LanguageTool extension made it drop down to normal levels and made Firefox responsive again. It looks like the extension might be doing some runaway processing somewhere?

I didn’t have any text field focused. I’m using version 8.3.0 with Firefox 121. Let me know if there’s any other useful debug info I can share.

Thanks for the report. Is there any way for us to reproduce this, e.g. by visiting a certain page? According to about:processes, extension use lass then 1% of CPU for me.

No, I understand that this is really hard to reproduce, but it didn’t happen with a particular page. It was happening while I was just switching tabs or even had the browser open in the background. Looking at my open tabs, potential culprits are Gmail and Google Calendar, possibly YouTube (though I’m fairly sure I’ve also encountered this without YouTube open).