Autotab 1.5.4

Fixes a critical bug when applying a filter more than once. Since Firefox sets the default maxLength on an text box to -1, Autotab did not account for this and never applied the default 2147483647. As a result, no characters would appear. Autotab also now applies only to an input with type of text. This will likely be expanded in the future when work is done to factor other form fields (#14).