For my work I use FF under OSX 10.6. I have another, older machine with OSX 10.7 Lion installed running around the clock in my living quarters. I use FF on it for trivial operations such as checking the weather report, quick searches etc. I also always test new versions on it before installing it on my work machines, so as not to risk any workflow problems. Soon after installing FF 27.0 I was very surprised to find that the machine running Lion was almost frozen, with 500Mb of free space left instead of the usual 45-50Gb. After some research, I figured that in the course of a few hours the swap files had multiplied to death — something I never, ever had experienced earlier. At first I thought that this was the result of installing several plugin updates (Java, Flash and Silverlight) at the same time as the FF update. But a couple of days later, the same thing began to happen again. Having left the window of the folder containing the swap files open in the Finder, I could not only see that they had multiplied, but I could also watch them disappear one by one after quitting Firefox. Installing FF 27.0.1 did not resolve this issue. But since going back to FF 26, the swap files have been staying put. I'll try again with 28, but until then I'm not going to run 27 on my work machines. I don't quite know how to get in touch with the developpers, so if anyone is there watching, please forward this to them.