I'm running a Mac (OS X 10.8.3) with Parallels (Windows 7) and have 1Password on "both" machines. Browser extensions are installed on all browsers, on both OS's, with one strange exception.
If I open IE 9 from the Windows start in Parallels, IE has the browser extension (I had to add the button to the toolbar myself, but now it's there & works)
When I'm using Safari on the Mac, and use the "Open current page in Internet Explorer" button to launch IE, the browser extension is not there, and I can't add the 1Password button to the toolbar. Since I can't explicitly install the browser extension in IE, I'm not sure how to fix this.