It was quite ok for the purpose I used it for, although not so comfortable to configure with its user interface, but now getting worse.
I am still using it as I don't want to look for an alternative due to time issues, but probably not so long anymore.

It really got worse with the version 5.

I rolled back to version 4.6.5 manually and deactivated the auto-update for this addon.
I lost all my settings due to the auto-update to version 5, which they also mention in the desciption of the new version - below - with saying sorry, but a sorry does not help.
The import function should work and should exactly solve the supposed "Firefox limitations" but it doesn't do..

Although the old design wasn't really good either, the new design is just a nightmare.
Besides that the new version displays my proxy password in cleartext on the screen - no way!