Click once on a mark. Hold down the shift key and click on another mark. Everything between those two marks will be selected.

Click once on a mark. Hold down the Control key and click another mark. Those two marks are now selected (but no others).

Awesome, Fred, this makes my day!. Many thanks!

So sorry, but when I click a bookmark it goes immediately to that webpage, I haven't yet found how to click a bookmark and still stay on the bookmarks list, (either right or left click) , so I've been unable so far to click 2 of them while holding shift. I've tried holding down shift before I click, either right or left, and no matter what it seems to take me to the bookmarked page, collapsing the bookmark column at the same time.

Will try some more, I'd like to be able to highlight a bookmark without it going to the page right away. Sorry to not get this so far but if there is a way forward please let me know, thanks

You have to do this from the full page Bookmarks Manager. <Control><Shift> B

That should do it. I'll report later in the day. Thanks again!