For a long time, I have experienced an issue when running Firefox in the i3 window manager. Although I still don’t know why the issue occurs, I finally have a good solution.

When I press the right mouse button, the context menu appears such that the mouse cursor is already highlighting the first item in the menu. Releasing the mouse button then immediately selects that item. This means that a simple right-click on a page takes me back to the previous page—the menu appears for just a moment, and the release of the mouse button selects the first item in the menu (the Back item).

I realized I can use userChrome.css to shift the context menu a few pixels away from the mouse cursor. Here’s the relevant excerpt from my userChrome.css file:

/* Offset right-click menus a bit so they don’t appear
   with the first item already highlighted */
#contentAreaContextMenu {
  margin-top: 5px !important;
}

This shifts the menu down by 5px, which is plenty to avoid the issue.

If you’re not familiar with userChrome.css, it’s a file you can create and add to your Firefox profile that tweaks the appearance of Firefox itself. It is frequently used to do things like change the location of the tab bar or hide unneeded menu items. If you want to learn more about this, there are a bunch of good resources at /r/FirefoxCSS.

Since userChrome.css relies on the internal names of browser components (#contentAreaContextMenu in this case), it's fairly likely to stop working in future Firefox versions. If that happens, it shouldn't be too hard to find the new name of the component used for the context menu.