Is you are Mac's user, if yes you can go to System Preferences > General > Show Scroll Bar > Choose "Always"

If not 1. go the search bar enter about:config 2. Hit and accept the risk 3. search side 4. Find and Change the following to 0

   layout.scrollbar.side

Hope this can help you

Thanks Junxian, for indicating that it is a feature of the OS. I have a windows-machine Unfortunately I cant find out what you mean by step: " 3. search side 4. Find and Change the following to 0 "  ??'In fact I already had search the configuration pages to find something about the glider/scrollbar, without any success.

I could access the option in another way : going to settings and asking for scrollbar. There I found that the option : hide scrollbar...." was already off .

My problem is something different: not the scrollbar itself, but the slider that is hidden, unless you can find it hovering . after is id found it shows itself. But when reading a long page, I don't want to play cat and mouse with the slider, it is terrible distracting.

In Settings The option "hide scrollbar ..... " is off. In the register there are 2 references both : "DynamicScrollbars"=dword:00000000.

But even in Registereditor the slider hides until you succeed in hovering over it, Crazy cat and mouse game !

Do you have this problem on multiple sites or just a specific site? I'm actually not sure how a site could hide a scrollbar, but it would be useful to know of an example.

There is a spam filter on links to non-Mozilla sites so please add a space before .com or otherwise break the link to avoid the delay of having your post moderated.

Now that I re-read your posts, I think designers call the movable item on the scroll bar the "thumb". Maybe there is a problem with lack of color contrast -- dark gray on light gray -- between the thumb and the bar?

Here's a screenshot of the colors I see for reference. Is this similar to yours? Possibly it varies depending on your theme.

On the new feedback website you can see scroll bars hidden by default that appear if you hover section and get wider if you hover the scroll bar.

I've seen cases as well, usually on pages with a dark background, where I'm not seeing the scroll bar probably because it has the same background color, but dragging in the area where it should be moves the page up and down.

The situation is exactly as jscher2000 indicated in his last post: the slider (thumb) is white on a white background, so you see nothing till you hoover over it, then it turns middle-grey. Only to hoover it you have to find it first, but it is invisible. Who had How can I have a slider (thump) that is visible all the time.I'm not interested in changing colours after I found it. None of the kind of simple theme's I like (i use Arctic Nord Theme ) addresses this issue. (the default system-theme has the same issue, but also it does not contrast the active tab against the inactive. So you have to guess your tab also.

HOW can have a thumb (slider) in my scrollbar in a permanent middle or darker grey without hoovering ? that is my question in the end.

Firefox generally tries to follow system colors when it comes to the scrollbar and many form controls. However, there is a way to use a style rule in the page to change the colors. For example:

/* Higher Contrast Scroll Bar Thumb */
html, body {
  /* thumb-color track-color */
  scrollbar-color: #888 #eee;
}

To apply style rules to web pages, you have two options:

(1) Use the Stylus extension (or similar extension)

This method is convenient because you can experiment with the colors and re-test in real time. However, it is another add-on:

https://addons.mozilla.org/firefox/addon/styl-us/

If you decide to try this, after installing Stylus, click its "S" button on the toolbar, then click Manage, then on the right side, click Write new style. Paste the above rule on the right side and give it a name on the left side. When you save the new rule, Stylus should start injecting it into you open tabs so you can see the result. Here's a screenshot after clicking Save.

On the downside, this won't work on certain sites where extensions are not allowed to inject code into pages, such as on this support site.

(2) Create a userContent.css file

This method is more involved, so I'll skip the details for the moment unless you want to try it.

Thanks jscher2000

Your solution works for most of the sites in Firefox. And that was my most urgent problem.

There is no Stylus for Thunderbird, but there the invisible thumb is less a problem for me.

I had liked to find out one day how to change this in Windows itself. But I Microsoft  pretend to know better what I need than I.  But they should allow to change colour-schemes