Users are experiencing major issues with Twitter and Firefox, in many cases completely unable to log in with the open-source browser.

According to 9to5Mac, multiple users have taken to Twitter to complain about not being able to log in to the social media platform using Firefox. In other cases, even users that are able to log in often have to continuously do so before it finally works.

At this point, it’s unclear what is causing the issue, although it seems to have started Monday evening for many users.

In my case, Firefox has not worked with Twitter’s login for the better part of a year, although it seems related to my use of privacy-preserving extensions and settings. That opens the possibility that individuals may be experiencing an issue related to such an extension or to a security change Mozilla has introduced in a recent version.