High CPU usage after second window is open

[hposca]

Hello there, recently I'm experiencing a high CPU usage after I open a second window.

I'm using the last version, "Multifox 3.2.2.1-let-fixed", and I realized this issue since firefox 43. (I'm using Linux Mint Rebeca 17.1 - 3.13.0-37-generic x86_64 GNU/Linux)

These are the steps that reproduce this issue on both my home and work computer:

• Open firefox
• Signin on first gmail account
• Start new profile (a new window with Ctrl-Alt-M)
• Signin on the second gmail account
• After this the CPU usage of firefox go beyond 100%

And, to certify that the problem is with multifox, I disabled all other plugins and tested only with multifox enabled.

Is this a known/expected issue?
Can I do something to help finding the culprit?

Thanks