There is nothing magic about web browsers, telent to port 80 at www.google.com and with a simple get request they will spit back their website. You can make it a little harder to do this stuff but a packet sniffer is always going to let you pretend to be any software you want unless they are using encryption. Also because Firefox is open source you can't prevent people from scripting using it anyway.
PS: I recommend all aspiring coders to telent to www.google.com at least once just to feel the magic.
It is recommended that you use the API that google provides for searching, but I fail to see why telnetting would be illegal. After all, both firefox and telnet use sockets to do their job.
Again, the comment above wasn't meant to be taken literally, but just because they both use sockets doesn't mean they're just as legal.
Imagine a web site which terms of service state you cannot use software to circumvent ads. Or where part of the security is done client-side (stupid, yes, but not impossible). Skipping the browser breaches at least the terms of service, and may be constructed as hacking. I think even Google discourages automated searching and prefers you use its api, which (at least some years ago) wasn't free for commercial use. I may be wrong in this particular case, but the important point is you may want to check the specific TOS before skipping the browser.
PS: I recommend all aspiring coders to telent to www.google.com at least once just to feel the magic.