Sorry to report that Firefox 140 for Windows has a bug that renders it vulnerable to crashing instantly on startup in the presence of certain third-party DLLs.

A 140.0.1 update is planned to fix the bug, but I don't know the schedule for release.

In the meantime, if Chrome or Edge isn't a good fit for you, maybe install the Extended Support Release of Firefox 128. Note that this installs in a separate program directory and needs to use its own profile (it won't use your Firefox 140 profile). https://www.mozilla.org/firefox/all/desktop-esr/

Firefox 140.0.1 is out. Firefox sets up a background process to update automatically, but to test sooner, you can install it now test whether it helps. Please let us know here, or you can comment in a thread on Reddit:

• Release notes: https://www.mozilla.org/firefox/140.0.1/releasenotes/
• To download an installer: https://www.mozilla.org/firefox/all/desktop-release/
• Feedback thread: https://old.reddit.com/r/firefox/comments/1ll0rps/firefox_14001_released_with_hopefully_fix_to/

If that doesn't help, some affected users have worked around the issue by renaming firefox.exe to something different, such as firefox1.exe. If you wanted to try that, the file is usually here:

C:\Program Files\Mozilla Firefox\firefox.exe

Renaming the file will break your normal shortcut, but after renaming, you can create a new shortcut:

• Windows 10: right-click firefox1.exe > Send to > Desktop (create shortcut)
• Windows 11: right-click firefox1.exe > Show more options > Send to > Desktop (create shortcut)

(The next update will create a new firefox.exe in the folder, so you'll need to remember to delete firefox.1.exe and its shortcut after that.)