What keeps happening to me, is I start a video mux or some disk intensive task, then I decide I want to look at something on the web. Firefox is not open. So, now I wait and wait and wait for Firefox to load since I only have 1 internal HD.
Determined to fix that I searched around and found a solution. Set up Firefox 3.6 Portable. Get a free Ramdisk program. After you have your Firefox Portable AddOns and other stuff set up and you know how much free disk space you need, set up your ram disk. After your PC starts and you have your ramdisk sitting there, just XCopy the whole Firefox folder into the ramdisk. Note that by default Firefox 3.6 portable has disk cache set to 0. I found setting it to 32 MB and allowing for that and a tad more in my ramdisk allocation really makes it snappier. I set my ramdisk to Fat32 128 MB which left me 125 MB of usable space. Plenty for the AddOns I use.
Assuming your Firefox portable is on C: and your ramdisk is T: you can run this as
a .cmd file:
XCOPY C:\PortableFirefox\*.* T:\firefox\ /E /Y /C
I call it LoadFirefox.cmd
If your ramdisk starts with Windows and always gets the same drive letter you could
put a shortcut to the .cmd file in your Startup folder. Otherwise just run the XCopy command or .cmd file from a command prompt or shortcut.
edit: I dragged a shortcut for the .cmd file to the Startup folder, then used WinPatrol delayed start feature to delay the xcopy 30 seconds on system start. It's working really well so far.
I have mine set up to discard the contents. No sense saving a cache to disk. Plus since NoScript changes(allow this site, that site) won't be saved, instead I rely on Sandboxie and just run the browser sandboxed right from the ramdisk. The sandbox will be made on your HD but that shouldn't really slow you down since your profile and cache and exe file are all in ram.
You can still download to the HD using Sandboxie "recover to folder of same name" options etc..