Type in accented letters, international characters, and various symbols into Firefox or Thunderbird, either simply by using a context menu (there being support for many languages French, German, Spanish, Italian, Esperanto, and so forth), or quickly by keyboard macro (you can even define your own). For example, the three keystrokes to compose e-circumflex are: e ^ INSERT. Or in two keystrokes as: e alt-F7.
The extension supports the CEN Multilingual European Subset, and was originally developed for European Language Day.
The extension can run with its default configuration, or choose languages and hot keys. To add language specific menus - from tools.abcTajpu tick the checkboxes for the languages you wish to appear in context menus, then click :-) for ok or X to cancel. Beyond that, power users can open tools.abcTajpu, and choose the radiobox for the hot key desired and suitable for your system (noting that this takes effect on newly opened windows). With a hot key setup (a function key or the insert key), you don't need to use the context menu, you can just type in an internet form for example a`INSERT to get a a-grave. (Not all hot keys will work with all systems or with all addons.) Finally, for the really keen, macros can also be defined in tools.abcTajpu -- a German speaker might choose "ss=%u00df|A[Ee]=%u00c4|ae=%u00e4|O[Ee]=%u00d6|oe=%u00f6|U[Ee]=%u00dc|ue=%u00fc" - now type (three keystrokes) AeINSERT for A umlaut.
There are fast hot keys, which can be turned off if they collide with other extensions. For example, alt-F2 for umlaut, alt-F7 for circumflex, alt-F8 for tilde, alt-F10 for acute, alt-F11 for grave.
When on a form, try alt-F1 (or shift-alt-F1) for a European keyboard. Also, control-alt-F1 to enter the hex number of any Unicode letter; and shift-control-alt-F1 to show the Unicode numbers of any selected text.