Fixed sidebar on Firefox mobile

[squidfunk]

Attempt to fix #8067.

[kamilkrzyskow]

I'd say LGTM, because the change does remove the gutter on mobile, I compared it with the previous commit 74a7835 which still had the bug. However, it sort of breaks when zoomed in on my PC, because there is a state where the CSS doesn't detect tablet mode, and where it has the drawer. I doubt you're targetting such case, but perhaps you could combine this tablet limiter with the ul change I mentioned in the issue where effect is a bit more subtle, I pushed the branch so you can compare if it's worthwhile to include ✌️

• https://github.com/squidfunk/mkdocs-material/tree/8067-firefox-scrollbar
  Note that apart of the screenshot, I didn't validate too much besides that, I'm only assuming that the ul scope is correct.

Works on mobile

Doesn't work with a specific zoom level on PC

[squidfunk]

Thanks for validating!

Media queries and zooming are an open problem, and it is a problem that is orthogonal to the matters discussed here. The media queries should actually handle text zoom, but browser zoom might be something different. Thus, I'd not consider this right now, but we'll look into it when we do the next complete makeover.