[Fx 141][default_tabs_photon_alt.css] Line under the active pinned tab

### Description of the Issue

I updated to FF 141.0, and the bottom border on the active pinned tab no longer disappears. I'm using a custom light theme and default_tabs_photon css.

### Does the issue occur with the most recent version of CustomCSSforFx (release/test/dev build)?

Yes, with the latest release

### Screenshots showing the issue

Now it looks like this:

It should be like this:

### System information

- Win10:
- Firefox 141:
- Firefox custom light theme (for example https://addons.mozilla.org/ru/firefox/addon/white-minimal/):

Start by reading default_tabs_photon_alt.css and inspect the rules affecting the active pinned tab's bottom border. Compare the current and expected screenshots; done means the border disappears for the active pinned tab when using a custom light theme on Firefox 141.

Written by the indexing model from the issue text.