Show error message and troubleshooting steps on contextual identities error

[brizental]

Before submitting your pull request

• I agree to license my code under the MPL 2.0 license.
• I rebased my work on top of the main branch.
• I ran npm test and all tests passed.
• I added test coverages if relevant.

Description

This is just a suggestion. See screenshot of what the error looks like:

Two things:

1. That is not a content suggestion. I couldn't come up with something good so I just added a sentiment there for now 🆘
2. I had no idea how to add new strings. I added something directly in the l10n submodule. Here it is, just for illustration purposes: https://github.com/brizental/multi-account-containers-l10n/pull/1/files

Type of change

• Bug fix
• New feature
• Major change (fix or feature that would cause existing functionality to work differently than in the current version)

Tag issues related to this pull request:

• Popup is blank when privacy.userContext.enabled is false #2597

[dannycolin]

I had no idea how to add new strings. I added something directly in the l10n submodule. Here it is, just for illustration purposes: https://github.com/brizental/multi-account-containers-l10n/pull/1/files

You can open a PR on the upstream l10n repository and simply mention that it depends on this PR to be merged.

That is not a content suggestion. I couldn't come up with something good so I just added a sentiment there for now 🆘

Looks good to me.

[dannycolin]

nitpick: I think we could use more obvious like containers-pref-error