Try following:

• Find the directory of your Firefox profile folder in the filesystem.
• In there, create a directory "chrome", if its not already.
• In that "chrome" directory, create a file "userChrome.css", if its not already.
• Add following code to the "userChrome.css" file:

.tabbrowser-tab {
  max-height: var(--tab-min-height) !important;
}

• Restart Firefox and look if its better for you.