scrubyt require firewatir gem to run but it doesn't specify it

$ cat simple.rb 
require "rubygems"
require "scrubyt"

$ ruby simple.rb 
/usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require': no such file to load -- firewatir (LoadError)
	from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
	from /usr/lib/ruby/gems/1.8/gems/scrubyt-0.4.06/lib/scrubyt/core/navigation/agents/firewatir.rb:2
	from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
	from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
	from /usr/lib/ruby/gems/1.8/gems/scrubyt-0.4.06/lib/scrubyt.rb:29
	from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:36:in `gem_original_require'
	from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:36:in `require'
	from simple.rb:2

$ sudo gem install firewatir
Successfully installed s4t-utils-1.0.4
Successfully installed user-choices-1.1.6
Successfully installed commonwatir-1.6.2
Successfully installed firewatir-1.6.2
4 gems installed
Installing ri documentation for s4t-utils-1.0.4...
Installing ri documentation for user-choices-1.1.6...
Installing ri documentation for commonwatir-1.6.2...
Installing ri documentation for firewatir-1.6.2...
Updating class cache with 3036 classes...
Installing RDoc documentation for s4t-utils-1.0.4...
Installing RDoc documentation for user-choices-1.1.6...
Installing RDoc documentation for commonwatir-1.6.2...
Installing RDoc documentation for firewatir-1.6.2...

I guess that firewatir should be added as dependency to gem specification.