RAMDISK Windows 10:

Install ImDisk Toolkit which will mount certain amount of the RAM as a virtual HDD.
http://reboot.pro/files/file/284-imdisk-toolkit/

Or install https://www.softperfect.com/products/ramdisk/ , it also does RAMDisk.

Install some synchronization software so you can synchronize ramdisk data with your HDD. (Ramdrive is just temporary storage and if there is power outage, you may loose ramdisk data.)

I used FreeFileSync from http://www.freefilesync.org/ and there are another Sync Tools: http://www.thewindowsclub.com/file-folder-synchronization-freeware
https://sourceforge.net/projects/synkron/

The resulting RAMdisk/RAMdrive i used to host FirefoxPortable + its profile folder which i pasted in my case into R:\FirefoxPortable\Data\profile. Into that folder belongs these entrie for example:
cache2
safebrowsing
addons.json
cookies.sqlite
extensions
extensions.json
I thinked about Samsung 850 Evo SSD purchase, but RAM is faster and already in my PC. // Firefox may still access C:\ drive because of some System32 dlls, fonts and others so it may make the program start slow and im still experiencing frozing or better say lagging of Firefox (running like 30tabs+). So tweaking Firefox caching is needed: about:config page and value "browser.cache.disk.capacity" maybe. Im unhappy with Firefox performance now even im using it on RAMdisk.

There is the performance comparison of the HDD, Truecrypt volume(HDD based) and RAM:

Name:  diskHDD5400_vs_TruecryptvsRAM800Mhz_io_performance_comparison.jpg
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Best RAMdisk performance i achieved this way in ImDisk application: NTFS as a filesystem, NOT allocate memory dynamically, NOT use AWE physical memory.

Synchronization software can then be setup to do synchronization between physical disk and RAMdisk.

In my case, while im having Firefox & its Profile on RAMdisk, i needed to prevent syncing of parrent.lock and entries folder as parrent.lock is locked when FF is open causing sync error and entries is the folder for cache files which i do not wish to sync as it takes alot of disk/ram space. So i added following exclude rules into the filter:
*\parent.lock
*\entries\*