hello sam

You can check for problems with the localstore.rdf file.

   http://kb.mozillazine.org/Corrupt_localstore.rdf

You can possibly disable placing the tabs in the title bar via the customize window.

You can also try to add this code to userChrome.css.

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

/* TAB - Pointer Events [74] */
#tabbrowser-arrowscrollbox {pointer-events: none}
toolbarbutton#scrollbutton-up, toolbarbutton#scrollbutton-down {pointer-events:auto}
.tabbrowser-tab, #tabs-newtab-button, .tabs-newtab-button {pointer-events: auto}
.new-tab-popup, .new-tab-popup > * {pointer-events: auto}  /*container tabs - longpress*/

See also:

• https://www.userchrome.org/what-is-userchrome-css.html
• https://www.userchrome.org/how-create-userchrome-css.html
• https://www.userchrome.org/firefox-changes-userchrome-css.html

There does not appear to be an option to control double-clicking behavior in the Customize windows. I noticed something though: this double-click-for-new-tab-behavior only occurs when browser.tabs.drawInTitlebar is False (the default is True). I had set this to False, as I want to have a titlebar, but this unexpectedly causes the tab area to behavior differently, it causes the tab areas respond to double-clicking by creating new tabs.

The CSS code for userChrome.css I posted above should disable the feature to open a new tab if you double-click in free space on the Tab bar, so you may want to give that a try.

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 plain text file with the name userChrome.css (name is case sensitive). In this userChrome.css text file you paste the text posted. On Mac you can use the TextEdit utility to create the userChrome.css file as a plain text file.

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 (Quit/Exit) and restart Firefox when you create or modify the userChrome.css file.

See also:

• https://www.userchrome.org/what-is-userchrome-css.html
• https://www.userchrome.org/how-create-userchrome-css.html

In Firefox 69 and later you need to set this pref to true on the about:config page to enable userChrome.css and userContent.css in the chrome folder.

• toolkit.legacyUserProfileCustomizations.stylesheets = true

See:

• https://www.userchrome.org/firefox-changes-userchrome-css.html