Why can't I paste my local .HTM file URL into the Validator filename

In order to validate one of my local XHTML webpages with Validator by Uploading my File, I used to be able to Paste the file address in the forms blank filename URL field, which took about a second.  Now I am forced to browse my directories to input the address of the file I want to validate, which can take up to 10 seconds.

The way I am now prevented from Pasting depends on the browser.  When in IE8 I right click over the Validator input form field in order to Paste a filename URL I have just copied, IE8 grays out the Paste.

When I right click over the input form field in Firefox 3, the file browser window is opened instead of the form's accepting the Pasted address.

Am I being hamstrung by some kind of local security setting or do I have the Validator website programmers to thank for wasting my time?  If the latter, does anyone know of any kind of workaround?