Actually useing option 2 on the link chouguard provided dose not in any way violate the Googel TOS it is not restricting the use of firefox but given informatin on the product and a link to download there is nothing stateing "clik the link" or any form of that and it also has a link sayin continue without firefox
Why would you want to show a faux-error-page to non-firefox users? I mean, who are you to force people to change their internet browser of preference (if using the level 3...) or generally be an annoyance with the level 1 or 2 packages just because you're using something and feel all superior about it? What about Opera? Safari? K-Meleon? Even Lynx...
The level 1 and 2 says "Click the button on the right to download Firefox. It's free" and that is encourageing. You are only allowed to write "sponsored links" by googles TOS.