Key combinations on mouse press stopped working in Firefox

[mutterstarb]

XMBC Version: 2.19.2
Windows Version: Windows 10
Mouse Information (brand/model): Cheap ~10 years old wireless Defender mouse, don't know the model as the sticker is completely erased (2 standart buttons, mousewheel press, 2 side buttons). Generic HID device drivers and no other mouse-related software.
Did the problem occur after an upgrade of XMBC? (If so, from what version?): No
Did the problem occur after a Windows update/upgrade? (If so, from what version?): No
How long have you used XMBC?: 2 days
What language and keyboard layout do you use in Windows?: Language: Russian, Keyboard: Russian and English.

Clear description of the problem - try and include as much information as possible, including what button and mappings you are having problems with (if applicable).:
Hello. I downloaded XMBC couple days ago, and mapped one of the side buttons to Ctrl+Shift+T ("Undo closed tab" in Firefox and Tor Browser). It was worknig fine at first, but today it just stopped (seemingly spontaneously).
As far as i can tell from my tests, the only thing that is not working are key combinations in firefox and tor (tested multiple different shortcuts); assigning a single keyboard button (F5) to mouse button DOES work in browsers; combinations DO work in other applications (tested in Notepad and Clip Studio Paint with several differen combinations).
Tried reinstalling XMBC, installing an older version, restarting Firefox, restarting PC, creating a profile specifically for Firefox instead of using the default one, changing keyboard language layout, nothing changed.
Any ideas? Thanks.

[phil]

No obvious reason for it to do this, can you turn on debug logging (in the settings / updates and logging tab) OK and APPLY that, then try again in firefox. Then send me a copy of the log file by PM (you can open the log file from the same setting tab - just copy/paste or attach the file to a PM/email).

Please be aware I am away over Christmas so I may not be able to have a look immediately, I hope it will be obvious from the log what is going on but that is not always the case and sometimes I need to look through the code which will be difficult while away.

[mutterstarb]

I sent you an email.