Use favicon API in Firefox

[flaksp]

Currently, we fetch favicons using our own Cloudflare Worker, which is fine for privacy, but not the best solution in terms of user experience and performance.

In Chrome, we use new favicon API (introduced later in Manifest V3). Unfortunately, there's no similar feature in Firefox yet. We should migrate to favicon API when it will be available in Firefox.

### Blockers
- [ ] Wait for resolution of the bug 1315616: "[Give extensions access to cached favicon URLs](https://bugzilla.mozilla.org/show_bug.cgi?id=1315616)"

### To Do
- [ ] Update code in `src/api/favicon` directory
- [ ] Bump minimal Firefox version in `.browserslistrc` file
- [ ] Bump minimal Firefox version in `webpack.config.js` file