Hi Ashish
The following link may be of help to you
https://support.symplified.com/entries/23702866-Enabling-IWA-on-Chrome-or-Firefox
It explains how to set up IWA with Firefox or Chrome.
In as far a SiteMinder is concerned If IWA is working properly with Siteminder on IE ,this means that your IWA integration is working properly with Siteminder .
According to the IWA authentication flow, it is IIS that negotiates the windows authentication, so you need a browser that supports sending windows credentials and that is configured properly to send those credentials automatically. In the documentation, mention is done of the Internet Explorer since this one obviously supports sending credentials automatically.
For the rest of the browsers it may be a matter of configuration or of support on the side of the browser vendor. For instance Chrome usually piggybacks on IE settings.
Regarding your questions in particular
1. The recommended settings in Internet Explorer are made so that windows authentication is passed to IIS automatically.
2. If the settings are not done, the credentials may not be passed correctly to IIS, and it may not be able to authenticate you, so authentication may fail
3. With some proper configuration and depending on the browser this may be possible. However, please bear once again in mind this is not a specific SiteMinder issue.
Hope to have helped
Miquel Gilibert