Recently, one of my clients with a Bobby AAA accessible site was informed that his PHP style switcher didn't work with a Linux/Mozilla 1.4 combination. This was troublesome since it's very important to him to be accessible not only to screen readers, but also to low vision users.
I attempted to get to the bottom of it and, with the help of Tom Pletcher here at Community MX, I found the page at Mozilla where you can download all the previous versions of the browser. I'm sharing it here just in case I ever lose my bookmarks 
… and so you don't have to dig for it if you need similar. Mozilla 1.x Releases will give you access to all Mozilla 1.x releases for all platforms. Handy!
Using these, we were able to download Mozilla 1.4 (2 years old) onto OS X and a PC — these showed no issues with the switcher. I found a friend with a Linux box that had Mozilla 1.7.8 installed — which also worked perfectly. I was able to convince him to install Mozilla 1.4 on that box to test for me (thanks Steve!) — It was also flawless. Thus, we determined the issue was on the person's computer that reported it which releived my client's mind. But without that great little link to the older versions of Mozilla, I would have been searching through Google for similar problems, likely taking more time than I could afford to give it with my workload of late.
