If you want to change your default Firefox homepage but it automatically reverts to www.tobii.com next time you open Firefox, one of the config files storing your browser preferences is most likely locked.
How to unlock homepage settings:
1) Close down all running Firefox windows
2) Open Windows Start-menu
3) Open Computer
4) Browse to C:\Program Files\Mozilla Firefox
5) Look for "Mozilla.cfg" (Mozilla CFG file)
6) Open Mozilla.cfg
*A window will open saying "Windows can't open this file"
7) Click "Select a program from a list of installed programs"
8) Press OK
9) In the next Window double click "Notepad" in the list
*A notepad with the contents of the configuration file will open*
10) Search for these two lines:
// set Firefox Default homepage
11) Remove these lines
12) Save the file.
13) Open Firefox
**You should now be able to change homepage in Firefox**
If this didn't help, please look through this article explaining other solutions: