I am experiencing this same problem. Firefox works great on my PC until I turn on Windows Speech Recognition. At that point, Firefox becomes completely unresponsive. Clicking on tabs doesn't change anything, keypresses (like CTRL-TAB) don't do anything, Firefox basically freezes. I have to turn off WSR and then kill Firefox and restart it for it to return to normal.

I have a brand new Surface Book 3 with 10th gen i7 processor and 32GB RAM.
Using FF 78.0.1 (64-bit)

OS Name Microsoft Windows 10 Home
Version 10.0.18363 Build 18363
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Manufacturer Microsoft Corporation
System Model Surface Book 3
System Type x64-based PC
System SKU Surface_Book_3_1899
Processor Intel(R) Core(TM) i7-1065G7 CPU @ 1.30GHz, 1498 Mhz, 4 Core(s), 8 Logical Processor(s)
BIOS Version/Date Microsoft Corporation 6.19.140, 4/13/2020
SMBIOS Version 3.3
Embedded Controller Version 255.255
BIOS Mode UEFI
BaseBoard Manufacturer Microsoft Corporation
BaseBoard Product Surface Book 3
BaseBoard Version Not Available
Platform Role Slate
Secure Boot State On
PCR7 Configuration Elevation Required to View
Windows Directory C:\windows
System Directory C:\windows\system32
Boot Device \Device\HarddiskVolume1
Locale United States
Hardware Abstraction Layer Version = "10.0.18362.752"
Time Zone Eastern Daylight Time
Installed Physical Memory (RAM) 32.0 GB
Total Physical Memory 31.6 GB
Available Physical Memory 20.9 GB
Total Virtual Memory 36.3 GB
Available Virtual Memory 23.8 GB
Page File Space 4.75 GB
Page File C:\pagefile.sys
Kernel DMA Protection On
Virtualization-based security Running
Virtualization-based security Required Security Properties Base Virtualization Support
Virtualization-based security Available Security Properties Base Virtualization Support, Secure Boot, DMA Protection, UEFI Code Readonly, SMM Security Mitigations 1.0, Mode Based Execution Control
Virtualization-based security Services Configured Hypervisor enforced Code Integrity
Virtualization-based security Services Running Hypervisor enforced Code Integrity
Windows Defender Application Control policy Enforced
Windows Defender Application Control user mode policy Off
Device Encryption Support Elevation Required to View
A hypervisor has been detected. Features required for Hyper-V will not be displayed.

Hi morpheus!
I'm trying to see if we can resolve some old bugs. Thank you for your report. Could you inform us if it still occurs on your end? If it is possible, could you try to reproduce it on latest Nightly version and tell us your input? You can download it from here: https://nightly.mozilla.org/.
Thanks!

Hi Marcela,
I am not the person you were responding to but I came upon this thread because I'm having the same issue as them. This issue is still occurring on my machine and I was able to reproduce it with the latest nightly version. I thought it might help to give my input since your comment was two months ago.

I notice this too just now. When I turned on windows speech recognition it appeared that the entire Firefox had locked up... didn't respond to any mouse clicks at all.. no idea why. According to Task Manager the task has not hung or crashed.

Same problem for me. Can't switch tabs or scroll pages. Putting recognition to the sleep mode unfreezes Firefox.

I also have this issue and can reproduce it using the following steps on Windows 10, but the steps should be similar to Windows 7 as well.

1. Start Firefox using your preferred method
2. Navigate to www.duck.com
3. Open Windows Speech Recognition by opening the start menu, searching for "Windows Speech Recognition" and selecting the result
   3a. optionally train the microphone, if you can skip this step and just get the floating microphone widget to appear onscreen then you've configured Windows Speech Recognition enough to start
4. Ensure Windows Speech Recognition is in Off mode by right-clicking the microphone icon and selecting "Off: do not listen to anything that I say"
5. Bring Firefox back into focus by clicking inside the application window
6. Activate Windows Speech Recognition listening mode by pressing Ctrl + Windows. The microphone should turn blue.
7. Attempt to right click inside the URL bar, observe no response from Firefox. Windows Speech Recognition may flash orange with a message indicating it did not understand what you said, even if you had your mic muted and no input. (I can only presume the message is misleading and WSR received some kind of error response?)
   7a. Optionally attempt to click around other controls in Firefox, observe they do not respond either and that WSR blips orange for a moment after you attempt the interaction
8. De-activate WIndows Speech Recognition by pressing Ctrl + Windows again. The microphone should turn grey.
9. After 10-20 seconds the URL bar context menu opens (if you did not do step 7a)

Expected results: Firefox continues to respond and I am able to use commands like 'show numbers' to expose input controls and type into textboxes using Windows Speech Recognition dictation.

Actual results: Firefox becomes unresponsive, freezing in terms of user interaction, but continuing to paint the window and appear to Windows OS to be responsive. Firefox acts as if the user were giving no input at all. 5-10 seconds after Windows Speech Recognition has de-activated, Firefox catches up to the last few interactions.

Redirect a needinfo that is pending on an inactive user to the triage owner.
:asa, since the bug has high severity and recent activity, could you have a look please?

For more information, please visit auto_nag documentation.

In the process of migrating remaining bugs to the new severity system, the severity for this bug cannot be automatically determined. Please retriage this bug using the new severity system.

Believe the severity here would be either S2 (because there is no workaround to using WSR on Firefox) or S3 (because using WSR is probably not considered a major Firefox feature).