Is there a Firefox extension that would block Washington Post popups at bottom RH corner of pages?

Install uBlock Origin

• Open Firefox for Mac and navigate to addons.mozilla.org.

• Search for uBlock Origin (by Raymond Hill) and click Add to Firefox.

Enable Annoyance Filter Lists

By default, content blockers focus strictly on advertisements. Enabling built-in "Annoyance" lists prevents bottom-corner slide-ins and floating widgets across news sites automatically:

• Click the uBlock Origin icon (red shield) in your Firefox toolbar.

• Click the Settings/Gears icon to open the dashboard.

• Switch to the Filter lists tab at the top.

• Expand the Annoyances section by clicking the arrow next to it.

   Check the boxes for:
        EasyList/uBO – Annoyances

        AdGuard Annoyances

   Click the orange Apply changes button at the top.

If a box still slips through

News websites occasionally update their layout code. If a specific popup ever persists after applying the steps above, you can remove it in two clicks using uBlock's built-in element picker:

   *Right-click directly on the unwanted box.

   *Select Block element... from the context menu.

   *A red highlight will cover the box; click Create in the lower-right preview window.

Firefox will save that rule permanently and prevent that specific element from rendering on any future visits.

Please answer my question above: "Is there a Firefox extension that would block Washington Post popups at bottom RH corner of pages?"

https://support.mozilla.org/en-US/kb/push-notifications-firefox https://support.mozilla.org/en-US/kb/push-notifications-firefox#w_how-do-i-revoke-the-notifications-permission-for-a-specific-site

The description of popups on bottom right corner sounds like these are just Web Push Notifications from sites you have allowed to send you notifications. You can block or revoke the site from sending you notifications as shown in the second KB link above.