Firefox add-ons sync messes up my active tab color

[Kratorator]

Hi,

• I'm not fluent in CSS at all
• I use the Windows accent color to identify which of three computers I'm at in remote desktop
• I set up Firefox active tab to the Win accent color on each computer by adding this in their "Extra Rules" box in TST options
  (Example for PC 1, the other two are off
  All code adapted from the TST website or others)

/---------------------------------------------------------------------------/
tab-item.active .background{
background: #CA5010 !important;
opacity: 1;
font-weight: bold;
}
tab-item.active tab-closebox:hover::before {
background: #CA5010;
display: -moz-box !important;
}
:root {
--multiselected-color: #CA5010;
--multiselected-color-opacity: 0.33;
} /---------------------------------------------------------------------------/

• Since I started syncing add-ons with Firefox sync, the latest change to TST "Extra Rules" spreads to the other two computers and my active tabs get the same color on all three PCs.

• So I cluelessly tried this: in userChrome.css, I put (example for PC 1 again)

/---------------------------------------------------------------------------/
:root {
--TST-tab-bg-color: #CA5010;
} /---------------------------------------------------------------------------/

and in the TST "Extra Rules" box, I replaced all the #CA5010 color values with
var(--ch_TST-tab-bg-color)

IT DOESN'T WORK, of course. I get a greyish turquoise color on the active tab (#46777E).

What's the correct way to solve this?

In advance, thanks a lot for your help.