I'm also using EXIF Viewer but as stand alone program. This way I drag photo from any web browser to the dock(on the icon of this little software) and EXIF data shows up...
I use this one as well, it's pretty handy as you don't have to leave the browser. Right click on an image, and if it's a supported type you get a "View Image EXIF data". Though more often and not the images I try it on don't have EXIF data, but oh well. I've tried one or two other extensions but this one seems the best.
If you have the file saved locally most image viewers (preview included) have an option like "View File Information/Properties" or something along those lines, and in the window that pops up you can see the EXIF data if it's available.