Re: Why are the bookmark icons on the home screen so rubbish looking?
Our design is constantly evolving. Feedback about things like this is helpful, so thanks! The web as we have it right now wasn't really designed well for phones and high-res displays. That's been changing steadily over the past few years though, and more and more sites are providing higher res artwork that we try and use. In some cases, sites are using webkit or iPhone specific markup to designate icons that are designed specifically to fit in on the iPhone and won't necessarily look good on Android.
We currently take the largest icon specified as a favicon (you can designate multiple ones at different sizes using the sizes attribute: https://developer.mozilla.org/en-US/docs/HTML/Element/link#Attributes), scale it to a certain size and place it on a background that is colored to compliment it. In some cases that works very well. In others its not perfect. We're working to reduce that. Specific examples of sites that are bad are helpful.
We have some bugs on file to improve our ability to find icons in ico files (https://bugzilla.mozilla.org/show_bug.cgi?id=419588), but as I mentioned we currently ignore other link tags designed to target other browsers. I think ideally we'd like to move to improving our ability to detect and use high res icons, and help encourage web authors to start specifying them in standard ways rather than using techniques that are targeted at a particular device or browser.
As a side note, you don't have to bookmark sites to add them to your homescreen in Firefox! Just load the site, long tap on the urlbar/page title and select "Add to homescreen".