So, this must be how Dell prep their PCs:
1) Get PC with no OS from Chinese manufacturer.
2) Open up the box, plug it in etc.
3) Configure BIOS and add service tag (some charges may apply).
4) Eject the DVD tray and put in Windows OEM disk.
5) Install Windows.
6) Update Windows.
7) Install each piece of Dell bloatware manually.
8) Install PowerDVD, Office Home trial, AV (free for a year or whatever) etc manually.
9) Install Firefox manually.
10) Run sysprep so that you get the out-of-box experience when the buyer switches it on.
1) to 3) as before:
4) Deploy the OS image containing the requested software onto the PC.
Now, if Firefox is on the OS image there is no difference between the way the purchaser gets Firefox and the way they get IE. Yet no-one would say that Dell installs IE on every Windows computer you buy from them, and imagine the mockery if Dell tried to charge users for IE installation. And as a choice needs to be made whether or not the Firefox image is used, the effective cost for each additional PC which has Firefox installed is about zero.
Now it may be that Dell are technically correct in a legal sense, but Mozilla's terms and conditions are there to prevent consumers being ripped off and this is exactly what they're trying to do. Dell are ripping customers off, plain and simple.