Firefox may repeatedly open new, empty tabs or windows after you click on a link, forcing you to close Firefox. The same untitled tabs or blank windows may open the next time you start Firefox if the previous session is restored.

This usually happens because you chose Firefox as the program to always use for a particular action, such as opening a certain type of file or launching an application to send mail.

Note: The Refresh Firefox feature can fix many issues by restoring Firefox to its default state while saving your essential information. Consider using it before going through a lengthy troubleshooting process.

https://support.mozilla.org/en-US/kb/firefox-repeatedly-opens-empty-tabs-or-windows

I ran the Firefox restore and that did not fix my issue. All of my settings seem to be correct. Any other suggestions?

Sounds as if you might have Firefox set for mailto. That doesn't work because Firefox "doesn't do email", although Firefox can work with web mail sites like Yahoo!Mail and Gmail. Just needs to be set up for mailto to open those web mail sites within Firefox preferences.

See if this support article helps you:
https://support.mozilla.org/en-US/kb/change-program-used-open-email-links

I have tried most everything to fix this. Just to reiterate ... I receive and email in Apple's imail that has a link imbeded in it. I click on that link. Firefox now (this did not happen in the past) simultaneously opens a window with my home Firefox home page and a second window with the page I am linking to. The home page window is behind the page I am linking to from the email. What used to happen is the home page would first launch and then that window would go to the page from the email link ... not opening two windows. I don't know how to stop firefox from launching two windows in this situation

This is a known bug on Catalina if you open a link from an external application.

• Bug 1600153 - macOS 10.15 Catalina - two firefox windows are opened when clicking on external link

(please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html)

Thank you!!

I'd just like to chime in...this is EXACTLY what is happening to me as well. Bought a new Mac, installed FF, double windows whenever FF isn't open and I click a link in email.

The only think I'd like to add is that I run Catalina on three other Macs, including my old MBAir, an iMac, and a six-month old Mini, and FF this is the first time I've run into this issue.

So are we waiting for Apple or Mozilla to fix?

Thank you, Pete

Does it make a difference if you switch to the default theme via customize mode in case you currently use the builtin light or dark theme ?

I just tried all of the modes and it makes no difference

This problem also exists with macOS BIg Sur beta 11.0.1.

Firefox is my default browser (of course), so when Firefox is "not" open and I click on any link (like in an email), two Firefox windows will open. One of them will contain the information related to the link, while the other window will be blank. In addition, within the FIrefox window that has the link information, I "cannot" open another tab. I must go to the "blank" window to use a different browser session.

The problem does not occur if a Firefox window is already open.