open about:config in the address bar
   set browser.cache.disk.enable to "false" (double click the line)
   verify that browser.cache.memory.enable is set to "true" (default value)
   add the entry (right click->new->integer) browser.cache.memory.capacity and set it to the amount of KB you'd like to spare, or to -1 for automatic cache size selection. (Skipping this step has the same effect as setting the value to -1.) [I skipped]
   profile backup using tar zcvfp ~/firefox_profile_backup.tar.gz ~/.mozilla/firefox/xyz.default
   creation of a script:

   Open Firefox.
   Click on the Firefox menu > Preferences > Privacy.
   Under “History,” select Use custom settings for history.
   Next to “Accept cookies from site,” click Exceptions.
   Under “Address of website,” type books.googleusercontent.com.
   Click Allow.

Dear Sirs, I tried to improve Firefox performance by following the steps at https://wiki.archlinux.org/index.php/Firefox_on_RAM In brief, open about:config in the address bar set browser.cache.disk.enable to "false" (double click the line) verify that browser.cache.memory.enable is set to "true" (default value) add the entry (right click->new->integer) browser.cache.memory.capacity and set it to the amount of KB you'd like to spare, or to -1 for automatic cache size selection. (Skipping this step has the same effect as setting the value to -1.) [I skipped] profile backup using tar zcvfp ~/firefox_profile_backup.tar.gz ~/.mozilla/firefox/xyz.default creation of a script: firefox-sync #!/bin/sh static=main link=xyz.default volatile=/dev/shm/firefox-$USER IFS= set -efu cd ~/.mozilla/firefox if [ ! -r $volatile ]; then mkdir -m0700 $volatile fi if [ "$(readlink $link)" != "$volatile" ]; then mv $link $static ln -s $volatile $link fi if [ -e $link/.unpacked ]; then rsync -av --delete --exclude .unpacked ./$link/ ./$static/ else rsync -av ./$static/ ./$link/ touch $link/.unpacked fi First execution of the script: $ killall firefox firefox-bin $ chmod +x ~/bin/firefox-sync $ ~/bin/firefox-sync Script calling every login and logout: echo '~/bin/firefox-sync' | tee -a ~/.bash_logout ~/.bash_profile >/dev/null After this Google Play Books fails with the error: Can't open book To read books on Google Play, set your web browser to allow cookies for books.googleusercontent.com. Learn more Firefox Open Firefox. Click on the Firefox menu > Preferences > Privacy. Under “History,” select Use custom settings for history. Next to “Accept cookies from site,” click Exceptions. Under “Address of website,” type books.googleusercontent.com. Click Allow. Did that many times. Kept failing. Restored the first setting set browser.cache.disk.enable to true again. Kept failing. Loaded again the cookie exeption for playbooks. Worked. Then I restored the disk.enable setting to false, and since that Google Play Books won't work anymore with either setting, cookie exeption or anything. I'll apreciate any guideline before the profile deletion; or if it helps you to improve Firefox I'll be glad to help. Regards, Nicolás Adamo