Your comments

Does it really crash or does it just not download the files? Did you check if the file is there?
It's optional because if you leave it empty it will try an anonymous login, for example for public ftp servers.
You can see the cause of this issue in the first comment:

Raw strings are explicitly set up to do regex pattern styling, so having a non-regex in a raw string will, as you see, mess things up.
(I'm not arguing for or against this behavior.)
Hello,

thanks for sending the file.

Textastic uses syntax definitions from TextMate. I tested your file in TextMate and it has the same syntax highlighting problem. 

This seems to be a known issue with regex highlighting in strings in the Python bundle. 

On Github, I found this issue: https://github.com/textmate/python.tmbundle/issues/1 - it doesn't seem to be fixed yet.
Can you please send me a small .py file that has this problem to support@textasticapp.com?
Thanks for the description of your idea. I understand that it's not only for JavaScript.

Regarding Firebug: Just follow the instructions on the Firebug Lite site. You need to reference it in the html code. If you download it and use the local link variant you can use it without an internet connection.
You can add the clojure TextMate bundle to add syntax highlighting support for it: https://github.com/swannodette/textmate-clojure

Racket can be found here: https://github.com/nkostelnik/racket-tmbundle


Have a look at the manual to see how this can be done.

For debugging JavaScript code, you can use Firebug Lite with Textastic. It also has a console for logging.
I had to find replacements for all syntax definitions when I completely rewrote the syntax highlighter. It seems like I didn't re-add a definition for clojure. But you can add the following TextMate bundle to add support for it: https://github.com/swannodette/textmate-clojure

Have a look at the manual.
You can add the clojure TextMate bundle to add syntax highlighting support for it: https://github.com/swannodette/textmate-clojure

Have a look at the manual to see how this can be done.