web form application using javascript

Question

In a C# 2010 web form application, I have found some JavaScript statements that will not allow the application to execute when I am using the Internet Explorer browser since some of the objects are obsolete/deprecated. However when I run the application using Firefox, I find that the application runs. I have also noted that some of the Javascript objects in the web form application may be deprecated in the future and to use these items with caution.

Thus if I deploy a new version of the current web form application and tell all users to only use Firefox in the next few weeks, I will create a static executable that everyone can use. Then when some of the objects are not allowed in Firefox, the application will still run since I have not changed the executable, correct?

Would I need create a new version of the application with the Javascript changes that are required?

If this is not true, would you let me know why and potentially what I should do to solve the issue?