Update to manifest version 3 + fix some event issues

[emanuelen5]

Thanks for this great plugin!

I fixed some small issues for myself, and thought I could upstream them if you want them also!

• The page stopped being wide after navigating around, and I had to either refresh the page, or toggle the plugin off/on. I fixed that by reapplying the style on each navigation.
• My browser complained that the manifest version 2 was deprecated, so I migrated it to version 3.
• One of the styles was a bit too specific and didn't match on all pages.

[emanuelen5]

Any update on if you want to merge? I've been using this fork myself since march and it works great (your plugin is really useful), so I think it would be nice to upstream it.

[emanuelen5]

Pushed an additional fix in 623bd07 that's needed nowadays to make PRs full width