Actually it explains very little. Please take a screen shot : https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem Then describe what you see wrong and what you expect.

dejvas said

Why a control appears after click on 'List all tabs' down arrow hasn't got a decent vertical (left) slider/slider bar?

A little rough on the English, but I think you're referencing the down-arrow at the far-right after the '+' sign?

I have a desktop with a wireless keyboard and mouse.

There are teenee-weenee-tiny vertical up/down scroll arrows. I hover the cursor over these arrows to active auto-scroll. The auto-scrolling is quite slow if you have a lot of Tabs in the browser window. For me, I currently have 620 Tabs in this main browser window! (I got some serious pruning to do.) The gray vertical bar at the right of a long list of Tabs is just an indicator of where you are in a long List of Tabs. It's not an active scrolling sliding bar.

I use my mouse's wheel to scroll through the 'List of Tabs'. Much faster. The Up/Down arrows on my keyboard also scrolls the List. Home/End keys snaps me to top/bottom of the List.

~Pj

Add code to the userChrome.css file below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

/* LIST-ALL-TABS - always visible */
#tabbrowser-tabs ~ #alltabs-button {visibility:visible!important}

/* SCROLLBOX - scroll bar */
.arrowscrollbox-scrollbox {overflow-y:auto!important}
.autorepeatbutton-up, .autorepeatbutton-down {display:none!important}

It is not that difficult to create userChrome.css if you have never used it.

The first step is to open the "Help -> Troubleshooting Information" page and find the button to access the profile folder.

• https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox

You can find this button under the "Application Basics" section as "Profile Folder -> Open Folder". If you click this button then you open the profile folder in the Windows File Explorer. You need to create a folder with the name chrome in this folder (name is all lowercase). In the chrome folder you need to create a text file with the name userChrome.css (name is case sensitive). In this userChrome.css text file you paste the text posted.

In Windows saving the file is usually the only time things get more complicated because Windows can silently add a .txt file extension and you end up with a file named userChrome.css.txt. To avoid this you need to make sure to select "All files" in the dialog to save the file in the text editor using "Save File as".

You need to close and restart Firefox when you create or modify the userChrome.css file.

. . . cor-el said

Add code to the userChrome.css file below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

Interesting. I already had and edited my userChrome.css file and added what you posted. Upon my next Exit/ReStart of FF, I'll see what goes.

I had a code in my userChrome.css for rounded Tabs, but something wasn't quite right with it so I deleted it. I've gotten use to the boxed Tabs now. (Grin)

~Pj

Question:

Is adding comments in a .css files using /* */ per each line or can it carry across multiple lines until the next '*/ ' is encountered? .

~Pj

Thx cor-el, you resolved quite well one of my Firefox troubles. How to fine-tune UI with userChrome.css has been beyond my knowledge before.

After applying of your work-arround, a fake and confusing slider still remain just left of the real slider (see this https://prod-cdn.sumo.mozilla.net/uploads/images/2018-08-13-22-43-54-9a2773.png).

As a matter of fact, this FF UI CSS (http://kb.mozillazine.org/UserChrome.css) adjustments are very cryptic and far from simple. So the next question is arising - why real slider isn't enabled by default? If one works with 100 or more tabs, it's uneasy, slow, sometimes error-prone (possibly cause of stop script dialog box and/or crashing down of the browser) or perhaps - always pretty painfull to navigate through just using up and down arrows on the 'list all tabs' scrollbox.

Kind Regards

I hadn't noticed that second bar before, but this bar appears to show what tabs are currently visible. You can check this yourself.

.alltabs-item[tabIsVisible] {
  /* box-shadow instead of background-color to work around native styling */
  box-shadow: inset -5px 0 ThreeDShadow;
}