Yes. I tested this on my WS 300, with Classilla 9.3.0 . My test site was http://www.spanishdict.com/'>http://www.spanishdict.com/
With the new default user agent it auto redirects to http://www.spanishdict.com/m
Whereas if I switch back to the old default agent, "Classilla 9.3.x" it stays at http://www.spanishdict.com/
Personally, I like this change as I've been manually switching to the mobile versions of sites anyway. However, there is a hardcoded list of sites that use the default "desktop" user agent by default. This is likely due to incompatibilities with their mobile site. (Sometimes the mobile versions are heavily catered to webkit mobile safari type browsers and use things Classilla doesn't have whereas their desktop site is fully, or at least more compatible.) You can probably override this by just typing the mobile site's direct address, but YMMV as it is probably whitelisted for a reason.