Solution applies to Windows.

1. Open My Computer.
2. Open following location C:\Documents and Settings\<user name>\
3. Open the Tools menu and click Options.
4. Click the View tab and ensure Show hidden files and folders is selected in the Advanced settings: section. Click OK to close the panel. 
5. A folder called Application Data should be visible. Open it.
6. Open the Phoenix folder.
7. Open the Profiles folder. 
8. Open the folder called "default". (If you are using another Firefox profile, open the folder matching the name of the Firefox profile you are using.) 
9. Open the folder whose name contains a strange sequence of characters and a .slt extension.
10. Find the chrome folder.
11. Rename the chrome folder to something else, like chrome-backup. 
12. Close the Explorer window and try and launch Firefox again.

If after this you get the same error, uninstall Firefox completely, and remove the folder you installed it into (e.g. C:\Program Files\Mozilla Firefox) completely, then reinstall Firefox.