Using same Firefox profile from multiple OS or PCs

To keep your Firefox profile consistent across multiple OS installs on the same PC, or different computers, you can use DropBox, as follows:

Make sure Dropbox is installed on all OS you are using. Move your Firefox profile folder into your Dropbox folder, and make sure it is included in selective sync settings.

If moving on Linux, make sure you use:
# cp -a /path/to/firefoxprofilefolder /path/to/Dropboxfolder

To make this work effectively though, pause syncing on Dropbox before you open the browser, so it won't be trying to write new files into the profile folder, and upload them to Dropbox at the same time.
Just let the profile files be updated on your local drive during a browser session, then after you close the session, resume Dropbox syncing to update the files online.

This way you not only have the bookmarks and open tabs syncronized, but also, all the addons and plugins you have installed, so you don't have to reinstall them in each OS.

Tip: Go into about:config and browser.disk.cache.enable to false, otherwise you create too many cache files on disk to sync. If you have plenty of RAM, disk caching is totally unnecessary.
And if you are booting off a flash drive, always have disk caching disabled.

To avoid having to have multiple copies of /Dropbox folder on separate partitions, move /Dropbox to a dedicated data partition that is mounted on boot, then add

mount -o bind /path/to/data/partition/Dropbox /path/to/local-directory

To startup scripts somewhere (like bootlocal.sh in tinycore)

Also, create user buttons in your file manager (like emelfm) to mount, and dismount the dropbox folder.