Fenix: [Bug]The uBlock add-on can be installed multiple times

[AndiAJ]

Steps to reproduce

1. Navigate to the Add-on manager
2. Tap the '+' (Add button) and confirm the addition
3. While uBlock is downloaded and verified tap again the '+' (Add button) and confirm the addition
4. While uBlock is downloaded and verified tap again the '+' (Add button) and confirm the addition
5. While uBlock is downloaded and verified tap again the '+' (Add button) and confirm the addition
6. While uBlock is downloaded and verified tap again the '+' (Add button) and cancel the addition
7. While uBlock is downloaded and verified tap again the '+' (Add button) and confirm the addition
8. While uBlock is downloaded and verified tap again the '+' (Add button) and confirm the addition
9. While uBlock is downloaded and verified tap again the '+' (Add button) and cancel the addition

Expected behavior

The '+' (Add button) should not be displayed while the Add-on is being installed and verified.

Actual behavior

The user can launch the installation process several times.
Or even cancel in between the whole process resulting in failure (based on the confirmation snackbar)

Device information

• Android device:

• Google Pixel 3a XL (Android 10)
• Google Pixel 3a (Android 9)
• Huawei Mate 20 Lite (Android 8.1.0)
• Samsung Galaxy S7 (Android 7.0.0)
• OnePlus A3 (Android 6.0.1)
• LG Nexus 4 (Android 5.1.1)

• Fenix version: Nightly #20370604 from 2/6

Notes

► Video

[AndiAJ]

Hi, this is still reproducible on the latest Nightly #20380605 from 2/7 using the following devices:
• Google Pixel 3a XL (Android 10)
• Google Pixel 3a (Android 9)
• Huawei Mate 20 Lite (Android 8.1.0)
• Samsung Galaxy S7 (Android 7.0.0)
• OnePlus A3 (Android 6.0.1)
• LG Nexus 4 (Android 5.1.1)

► Video

@gabrielluong - Please review. ☺️
I'll remove the QA needed label and reopen the issue.

[Amejia481]

@AndiAJ @gabrielluong put a patch for it, would you mind retesting? :)

[AndiAJ]

Hi, verified as fixed on the latest **Nightly #20410606 from 2/10**using the following devices:
• Google Pixel 3a XL (Android 10)
• Google Pixel 3a (Android 9)
• Huawei Mate 20 Lite (Android 8.1.0)
• Sony Xperia Z5 (Android 7.0.0)
• OnePlus A3 (Android 6.0.1)
• LG Nexus 4 (Android 5.1.1)

►Video