I like the wavy salmon background. It's low-contrast enough that it doesn't obscure the text on inactive tabs, bright enough to still make an impact, and the lines themselves are thick enough that they don't compete in scale with the tab text. Also, the palest colour goes well with it too, especially with the dark red - very readable on the active tab. The dark green goes nicely in the palette as well. I'm so-so on the url bar standing out so much but it's definitely on-theme and the colour palette is great.

I have some suggestions that would bring this up to 5 stars. Rating 3 stars for poor readability as I can't actually use this theme despite my appreciation for it.
- The dark green is a great high contrast nori colour next to the salmon, but it's too low contrast when actually used for text and other small elements. I suggest that background tabs have a translucent pale colour (such as the lightest one in your palette) over them to increase readability for the dark green text, by increasing contrast. The active tab can still stand out, but others should still be readable.
- Similarly, the bright salmon colour doesn't read well in the search/url bar. These are two mid-tone colours. I would change the text colour to the lightest tone as well and see if that helps. Remember that the green background acts as a dark/night mode, and dark mode tends to require thicker or larger text to maintain readability. Also, in the theme creation tool, all you have to work with is horizontal lines that indicate where the text would go in the url or tab. That's fine for a colour palette but not very useful for determining readability. Not only that, Firefox also dims out the non-domain parts of a url, which makes this even harder to read. I do love the look otherwise, but try using the lightest tone instead of the brightest tone for the text and see if that helps.