Join the AMA (Ask Me Anything) with Firefox leadership team to talk about Firefox priorities in 2024. Mark your calendar! Thursday, June 13, 17:00 - 19:00 UTC.

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

Happily used Firefox for 2 years, suddenly it won't open - getting this error message: "Platform Version incompatible with minversion >=1.9.1.11 maxversion <=1.9.1.11" What can I do?

  • 1 reply
  • 19 have this problem
  • 2 views
  • Last reply by TonyE

more options

Before this happened, I was having a problem for about a month where Firefox wouldn't close. I'd close the browser window, and later when I tried to reopen it to connect to the Internet, I 'd get a msg saying that Firefox is already running, and I must close the current window before opening a new one. I'd have to restart my computer at this point. I don't know if this is related to why I can no longer use Firefox at all.

Before this happened, I was having a problem for about a month where Firefox wouldn't close. I'd close the browser window, and later when I tried to reopen it to connect to the Internet, I 'd get a msg saying that Firefox is already running, and I must close the current window before opening a new one. I'd have to restart my computer at this point. I don't know if this is related to why I can no longer use Firefox at all.

All Replies (1)

more options

The "Platform version incompatible" error message can be caused by a problem with the installation of Firefox. Remove your current installation of Firefox and re-install.

  1. Delete all the files and folders inside the Firefox installation directory - C:\Program Files\Mozilla Firefox\
  2. Download the latest installer from Mozilla and install it.

Doing the above will not remove your bookmarks, passwords etc, since they are stored in a separate folder.

If after re-installing you get the "already running" error, see "Firefox is already running but is not responding" error - How to fix.

Modified by TonyE