https://bugzilla.mozilla.org/show_bug.cgi?id=69687

https://bugzilla.mozilla.org/show_bug.cgi?id=616108

https://bugzilla.mozilla.org/show_bug.cgi?id=676500

Despite the fact that the oldest of them is more than 19 years old, no real progress is made. Manual language switching is required and this is a usability nightmare for everyone who uses a more than one language simultaneously. For example, for me is a common practice to write messages in my native language and to mix English terms in them. The lack of this feature is the main reason for me switching back to Chrome, after I had returned to Firefox when Firefox Quantum was released. I suspect that only the lack of this feature is the main reason for many other people to not use Mozilla's browser and that this is a huge damage on their user base.

After all, for the feature to work the same way as in Chrome, does not look very difficult. The algorithm can be simply:

  function check(word, active_dictionaries):
    for dictionary in active_dictionaries:
      if word in dictionary:
        return true
    return false