In the days when it is not unusual to have 32GB RAM I would like to see installing programs directly to RAM keeping a copy of the program of HDD. RAM modules are very cheap today and users can ask - how can I use such huge memory?
It is not just about Firefox, but also other programs like Thunderbird. The idea is that user can create RAM disk and upload the files which he uses often to the RAM. So execution of Firefox, Thunderbird and other programs should be much faster. So I would like to see Firefox going in this direction. You could install Firefox not only to HDD but also to RAM disk. It would be related each other, the Firefox could choose which working folder to use, which profile folder to use and could synchonize writing data to RAM and disk. I run my PC 24h per day and so I feel not problem to keep every file in RAM if it would be backedup in the HDD.