userChrome.css

.tab-background {
  border-radius: 6px 6px 0 0 !important;
  margin-block: 0 !important;
  outline: none !important;
}

.tab-background:is([selected], [multiselected]) {
  box-shadow: none !important;
}

#nav-bar {
  border-top: 0!important;
}

/* -- OPTIONAL -- */
.titlebar-spacer[type="pre-tabs"] {
  width: 30px !important;
}
.titlebar-spacer[type="post-tabs"] {
  width: 0 !important;
}
#alltabs-button {
  display: none !important;
}

How do you add this to firefox?

@doseofmazen

• Go to about:profiles -> Open Root Directory of your profile -> Create folder chrome -> create file userChrome.css -> add above css
• Mozilla recently disabled userChrome.css to run by default. So, Go to about:config -> searchtoolkit.legacyUserProfileCustomizations.stylesheets -> set it to true
• Restart the browser.

Hi, the multi account container toolbar is not visible while the light theme is on
Do you know how to change its color so it shows up while the light theme is on.
Here is the same icon on dark theme:

left same comment here: https://gist.github.com/dumindu/28e4312b38b91fbfb9b701c41ccc5b66#gistcomment-3380129

@deepdmistry This is because, they are using light color icons on light theme.

However, are you using the userChrome.css?
If yes, please append the following css code to your userChrome.css and restart the browser.

#_testpilot-containers-browser-action{
  filter: invert(42%) !important;
}

Hey thanks so much for your help, that worked :)