The DragNDrop Toolbars add-on can be used to move toolbars up and down.

You can not fit two toolbars on the same row, but depending on the toolbars, you may be able to move the icons from one toolbar onto another. For details on how to do that see how to customize the toolbar.

Why are you still using such an old version of Firefox, which isn't even the last of the 3.0.x versions?

Firefox 3.5 was released in June 2009, Firefox 3.6 in Jan 2010, and Firefox 4.0 is due in December.

3.0.13 was issued in Aug 2009 - 3.0.19 was the last of the 3.0.x versions, and it was released mid-March 2010. Support has ended for the 3.0.x versions.

Thank you, dear "the-edmeis..." , for telling me about newer versions. The reason is very simple : I installed FF a (long) time ago, but I didn't like it at all because the Roboform toolbar could not be used at that time. I didn't use FF until now, although I it remained installed.

By the way, I see in my old version (in menu Help) a revolving icon indicating an ongoing process "Downloading Firefox 3.0.19 ..." . It is strange that this download actually never ends !

Besides, there is a difference with Linux, where updates are automatically announced for installed programs. I will install now the latest FF in Windows.

Still I dislike the fact that FF needs more rows to display toolbars as other browsers, where toolbars can be moved side by side on a row.

For the updating issue you can look at: http://kb.mozillazine.org/Software_Update (Software Update not working properly)

Remove the files in the updates and updates\0 folder:

C:\Documents and Settings\<user>\Local Settings\Application Data\Mozilla\Firefox\Mozilla Firefox\updates (%USERPROFILE%\Local Settings\Application Data\Mozilla\Firefox\Mozilla Firefox\updates)

C:\Program Files\Mozilla Firefox\updates

I updated to latest version. There is an interesting point I want to mention. The update made a warning that Roboform Toolbar would not be compatible with the new version.

However after FF update ... surprise : Roboform toolbar remained visible (in full version with all usual icons operative). I don't know why, but I don't care to know ... since it works !

To come back to the topic issue, this toolbar can't be moved to the top row (next to "Help", where there is space enough) Nothing is perfect. Thanks again for your provided help.

You can move items from the Navigation toolbar and the Bookmarks to the Menu bar if you want to use that space, but you can only move contents from other toolbars to a new toolbar or the Menu bar and Navigation Toolbar if that toolbar supports it. You can check that in the Options of that toolbar in Tools > Add-ons > Extensions.

Firefox toolbars are more customizable than with other browsers, the trick is that you don't move an entire toolbar all at once - you move the individual elements or buttons from one toolbar to another.
https://support.mozilla.com/en-US/kb/How+to+customize+the+toolbar

When it comes to toolbars provided by an addon /extension, the ability to customize it has to be provided by the developer of that addon with the proper code in that extension. (Rough guess is that it takes 3 to 4 times the amount of coding to create a toolbar extension that is as customizable as the 3 default toolbars.) If the developer did a quick and dirty job, you're stuck with a toolbar that wastes space.

One more tip. If you can't move individual toolbar items from a particular toolbar, see if you can move some other toolbar items to that toolbar. Then you could hide a different toolbar to save space. You need to experiment with your selection of toolbars to see what is possible.

Personally, when I configure a Firefox Profile I usually reduce the toolbars down to one visible toolbar, by moving the necessary elements up the the Menu bar (Tiny Menu extensions to reduce the default Menu buttons down to one). Elements I need occasionally are placed on the Navigation bar which is hidden (un-checked in the View > Toolbars menu) until I need to access one of those buttons.

The upcoming Firefox 4.0 looks like it is going to be a lot better at reducing UI space, allowing for a larger content area.

Thank you for this valuable information and the tips to be tried out.

Regarding the re-size part, may I confirm that as a windows user I like the option to hover the side of the Start bar and when mouse changes to spliter I simply click and stretch. That's what I what I would to have done to the Bookmark toolbar.