I use the add-on extension called Xmarks on Firefox, but I'm still using Ubuntu
Gnome 10.10. Since my other computers are using Chromium, I'm trying to decide
if I should use it or the Gmail account sync, but I use mostly Yahoo Webmail.
Any advice from others?

Bit of a mixed bag of questions there but here goes:

XMarks just saves Firefox bookmarks and it doesn't matter what OS you
are using ( Windows or Linux ) as the plugin is a Firefox one.

If using Chromium to view GMail then there's nothing you need to do to
save setting / mail etc... everything is stored on GMail servers and
you can access from any browser on any platform ( Windows or Linux or
Mac ). Same with Yahoo Mail - it's web mail and nothing is stored on
the PC itself.

AFAIK - GMail account sync is for sharing contacts etc between GMail
accounts you have. If you only have one GMail address it's of little
use :-)

Does that help ?

It seems there is an Xmarks for Chrome/ium, too. This is where I'd like
comments, there are both pros and cons for its use. I donated to Xmarks, so I
could use it for open tabs, too.
I was again reminded of my Windows background when my PcLinuxOS LXDE install got
corrupted or something. I got my files in Home off the SCSI hard drive via
Puppy, but have no idea how to find either Firefox or Chromium info in this
situation. I was making use of an old server motherboard and Firefox is too slow
on it, hence I was not aware of Xmarks for it at the time.
I installed the newer PcLinuxOS LXDE successfully and noticed there is an option
for a text file of History saved. Is this similar to what we find on Windows
computers for bookmarks in a HTML file?
In situations like mine backing up from a working Firefox or Chromium is out of
the question, or am I wrong. That's why I try to use Xmarks to save that stuff
off the computer, but with the rapid advancement of web browsers, I wonder...

FF is under rapid development. They switched the way they handle bookmarks
etc. switching from an xml file to a database. 10.10 probable used the old
way, but newer versions use the newer method. So if you have your bookmarks
in the old bookmarks file and a newer version of FF is looking for them in
an sql database them having the bookmarks file is of no use.

The way around the problem is to export the bookmarks then to import them
into the new version of FF.

I am not sure if this is your problem, but it sounds similar to one that I
encountered awhile back.

Almost correct - it's the *contents* of the profile folder you need to
copy to the new one, and you can safely delete the entire contents of
the new profile folder first :-)

Oh, forgot to mention it, I'm using 10.10.

In Firefox, "Organize Bookmarks," select "import and backup," "backup." Tell it
where to save the .json file. Stash it on a flash drive or other backup media.
On a fresh install, import that file.

As Roy points out, when you deal directly with any program's internal files,
there is always the chance that the format changes, and then you are out of
luck.

I follow a similar approach with Evolution: export from the old, import into the
new.

I did llike, in Google did a search for “restoring FF
profiles” and came up with
http://support.mozilla.com/en-US/kb/Profiles

Digging deeper into that page gave me
http://support.mozilla.com/en-US/kb/Backing%20up%20your%20information

I'm using FF 3.6. I weeded through all that info and made my own version of
it and saved in a text file. Here is what is in it (Kind of long but more
or less what Mozilla said about it.)


Locate your profile folder
The default location of the Firefox profile folder is
~/.mozilla/firefox/xxxxxxxx.default/.
xxxxxxxx represents a random string of 8 characters.

You can locate your profile folder using these instructions:
Firefox 3.6
1. At the top of the Firefox window, click on the Help menu and select
Troubleshooting Information.... The Troubleshooting Information tab will
open.
2. Under Application Basics, click on Open Containing Folder. This will
open the profile folder (e.g., the xxxxxxxx.default folder).

Backing up your profile
To back up your profile, first close Firefox if it is open and then copy
the profile folder to another location.
1. At the top of the Firefox window, click on the File menu and select
Quit.
2. Locate your profile folder, as explained above.
3. Go to one level above your profile's folder, i.e. to
/~/.mozilla/firefox/
4. Right-click on your profile folder (e.g. xxxxxxxx.default), and select
Copy.
5. Right-click the backup location (e.g. a USB-stick or a blank CD-RW
disc), and select Paste item.

Restoring a profile backupBacking up your profile
1. At the top of the Firefox window, click on the File menu and select
Quit.
2. If your existing profile folder and profile backup folder have the same
name, simply replace the existing profile folder with the profile backup,
then start Firefox.
Important: The profile folder names must match exactly for this to work,
including the random string of 8 characters. If the names do not match or
if you are restoring a backup to a different location, follow the steps
below.

Restoring to a different location
If the profile folder names do not match or if you want to move or restore
a profile to a different location, do the following:
1. Completely close Firefox, as explained above.
2. Use the Firefox Profile Manager to create a new profile in your desired
location, then exit the Profile Manager.
Note: If you just installed Firefox on a new computer, you can use the
default profile that is automatically created when you first run Firefox,
instead of creating a new profile.
3. Locate the backed up profile folder on your hard drive or backup medium
(e.g., your USB-stick).
4. Open the profile folder backup (e.g., the xxxxxxxx.default backup).
5. Copy the entire contents of the profile folder backup, such as the
mimeTypes.rdf file, prefs.js file, bookmarkbackups folder, etc.
6. Locate and open the new profile folder as explained above and then close
Firefox (if open).
7. Paste the contents of the backed up profile folder into the new profile
folder, overwriting existing files of the same name.
8. Start Firefox.

Starting the Profile Manager
Important: Before you can start the Profile Manager, Firefox must be
completely closed.
1. At the top of the Firefox window, click on the File menu and select
Quit.
2. In the Terminal run:
firefox.exe -p

If the Profile Manager window does not open, Firefox may have been running
in the background, even though it was not visible. Close all instances of
Firefox or restart the computer and then try again.
Creating a profile
1. To start the Create Profile Wizard, click Create Profile... in the
Profile Manager.
2. Click Next and enter the name of the profile. Use a profile name that is
descriptive, such as your personal name. This name is not exposed on the
Internet.
3. You can also choose where to store the profile on your computer. To
choose its storage location, click Choose Folder....
Warning: If you choose your own folder location for the profile, select a
new or empty folder. If you choose a folder that isn't empty and you later
remove the profile and choose the "Delete Files" option, everything inside
that folder will be deleted.
4. To create the new profile, click Finish.

Removing a profile
1. In the Profile Manager, select the profile to remove, and click Delete
Profile....
2. Confirm that you wish to delete the profile:

Don't Delete Files removes the profile from the Profile Manager yet
retains the profile data files on your computer in the storage folder, so
that your information is not lost. "Don't Delete Files" is the preferred
option because it saves the old profile's folder and allows you to recover
the files to a new profile.
Delete Files removes the profile and its files, including the profile
bookmarks, settings, passwords, etc.
Warning: If you use the "Delete Files" option, the profile folder and files
will be deleted. This action cannot be undone.
Cancel interrupts the profile deletion.

Renaming a profile
1. In the Profile Manager, select the profile to rename, and then click
Rename Profile....
2. Enter the new name for the profile. Type in the new profile name, and
click on OK.
Note: The folder containing the files for the profile is not renamed.