Random useful and not so useful hacks.

Fix your Firefox 1

1. Browse to your Firefox profile directory.
2. Create a folder named chrome.
3. Create a file named userChrome.css and add the following:

   .titlebar-color{
       color: -moz-accent-color-foreground;
       background-color: -moz-accent-color;
   }
   .tab-background{
       border-radius: 0px 0px !important;
       margin-bottom: 0px !important;
   }
   .tabbrowser-tab:not([selected=true]):not([multiselected=true]) .tab-background{
       background-color: color-mix(in srgb, currentColor 40%, transparent);
   }
   menupopup > menu, menupopup > menuitem{
       padding-block: 2px !important;
   }
   :root{
       --arrowpanel-menuitem-padding: 2px !important;
   }
   			

4. Enter the about:config in the URL bar to open the config page.
5. Filter to toolkit.legacyUserProfileCustomizations.stylesheets and set that option to true.
6. Restart the browser.

See also:

• userchrome.org
• winaero.com - Enable Loading of userChrome.css and userContent.css in Firefox

Fix your Firefox 2

about:config on Firefox Mobile: chrome://geckoview/content/config.xhtml

Fix your Thunderbird 1

In Windows explorer, navigate to `%appdata%\Thunderbird\Profiles`, and then into the `XXXXXX.default` subfolder.

• Create a new subfolder named `chrome`, and then navigate into it.
• Create a text file named `userContent.css` and leave it empty.
• Create a text file named `userChrome.css` and paste the following text into it:
  

  /* Global UI font */
  * { font-size: 11pt;}
  * { font-family: "Calibri";}
  
  .titlebar-color{
      color: -moz-accent-color-foreground;
      background-color: -moz-accent-color;
  }
  .tab-background{
      border-radius: 0px 0px !important;
      margin-bottom: 0px !important;
  }
  .tabbrowser-tab:not([selected=true]):not([multiselected=true]) .tab-background{
      background-color: color-mix(in srgb, currentColor 40%, transparent);
  }
  menupopup > menu, menupopup > menuitem{
      padding-block: 2px !important;
  }
  :root{
      --arrowpanel-menuitem-padding: 2px !important;
  }
  		

Fix YouTube

This will go back to the small thumbnails on the home page.

• Install uBlock Origin.
• Go in to uBlock Origin Settnings.
• Add the following at the end of the page My filters

! YouTube 5 Videos Per Row Fix (Home and Channel Pages)
youtube.com##ytd-rich-grid-row:style(display:contents !important;)
youtube.com###contents.ytd-rich-grid-row:style(display:contents !important;)
youtube.com##ytd-rich-grid-renderer:style(--ytd-rich-grid-items-per-row: 5 !important;)
! YouTube 5 Videos Per Row Fix (Channel Page margin fix)
youtube.com##ytd-rich-item-renderer:style(margin-right: calc(var(--ytd-rich-grid-item-margin)/2) !important; margin-left: calc(var(--ytd-rich-grid-item-margin)/2) !important;)
! YouTube 5 Videos Per Row Fix (Font Size fix)
youtube.com###video-title.ytd-rich-grid-media:style(font-size: 1.4rem !important; line-height: 2rem !important;)
youtube.com###metadata-line.ytd-video-meta-block:style(font-size: 1.2rem !important; line-height: 1.8rem !important;)
youtube.com###video-title.ytd-rich-grid-slim-media:style(font-size: 1.4rem !important; line-height: 2rem !important;)