I'm pretty new to illustrator, and I'm making myself a website. I made a graphic and then used the save to web function. I did a few different graphics and saved them as gifs because I wanted them transparent. Then I did some research on how to remove that "halo", and put a matte on it (black, the background of my page). However, now when I saved it as a gif, it showed up on my desktop with the little safari icon, not the gif icon (I can open it in preview, but the default is safari). It still ends in .gif though. Also, when I right click and select "save image" on my website, it wants to save it as a png. I double checked illustrator, and I definitely saved it as a gif, but that's not what it's showing up as. This is probably a very simple question, but what format is my image.. is it png? and why won't it save as a gif anymore? If it is png, is that a format that can be viewed by anyone on most browsers?
Kudos on the GIF/matte discovery!
PNG with transparency can be viewed "correctly" in most browsers, but not all, some will show white instead of the transparency. Further, PNGs store gamut info, so the Mac/PC gamut difference could be problematic when you need a smooth blend. I'd stay with GIFs, for your purposes.
As far as the format change issue, I'm not sure, but I'd recommend you set your OS to display file extensions so there are no questions.