It sounds like a file of line of code is corrupt. Please try reinstalling the beta version of Firefox.
Sorry for any inconvenience.

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove Firefox program files and then reinstall Firefox. Please follow these steps:

Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from http://www.mozilla.org and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

Please report back soon.

Same problem with the Release Version on Linux Mint 15. Downloaded from the official Ubuntu Repository.

hello kado456, can you replicate this issue when you launch firefox in safe mode (by holding the shift key while firefox is launching)?

Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

edit: it might also be important to know which language version of the browser you are using...

Hey so it looks like this was a bug that was resolved, but if you are still seeing it would it be possible to request.

[https://bugzilla.mozilla.org/show_bug.cgi?id=933626] In the bug, one of the users fixed this error by launching Firefox in safemode:

firefox.exe -safe-mode

and getting rid of this file" "English (GB) Language Pack 25.0"

Did that resolve the issue in the 26.1 version?

Hi phillip an rmcguigan, thanks a lot for your speedy replies.

Starting it with the safe-mode parameter fixed it.

I could not find the exact file you mentioned "English (GB) Language Pack 25.0" only sth similar, but I just downloaded the firefox-locale-en 26.0 separately and after installing this, it starts up without any problems.

So I assume that the problem was an outdated language pack.

I have to admit I did not know I needed to update this separately, so please accept my apologies for not trying this earlier. Nonetheless I am very grateful for your very helpful advice and glad I can run FF again.

I am running 26.0

Cheers, kado456

hey kado456, thanks for reporting back (& no need to apologize at all)!
since apparently there are quite a lot of users affected by this at the moment, your reply & confirmation how to solve the issue will be helpful to others in the same situation too...

Just to be clear, there is no Firefox 26.1 version as based on the OP date at time it was the 26.0b1 or 26.0 Beta 1 of ten Betas.

The current versions are now Firefox 26.0 for Release and 27.0b1 on Beta channel.