Seems you have both active which causes a conflict so reverts to the onboard GPU. Suggest enter your bios and disable the onboard Video card and then look to make sure AMD is set to Active and reboot. I would think this will solve your problem. If so please come back and mark as solved or......

I saw a suggestion like this in reference to another post, but then questions were brought up about the usage of the computer.

Will this cause any negatives? I do regularly use an external monitor for multi-screen use off of the HDMI, and occasionally I hook up to 2 externals (1 via a Toshiba dynadock through the USB, the other through the HDMI).

Thank you for your help

NO it should not cause any issues as it is a conflict issue that both are running at the same time. Though most times it does not matter but in your case since having issues this is the place to start. I also have onboard video and disable it. If you do have issues with your other connections after disabling it you can always re-enable it. It may affect your docking but by HDMI cables it should not. Only way to know is disable the onboard video and to dock it.

Please come back and let us know if this worked and mark as solved if this solution works.

Thanks for the help. I went to try and disable the main card in the bios, and much to my suprise, there were no graphics options in the bios.... Not sure if I missed something or things changed, but I've never seen so little control in a bios system.

Used the following method to access the bios on my windows 10 laptop.

   Navigate to settings. ...
   Select Update & security.
   Select Recovery from the left menu.
   Click Restart Now under Advanced startup. ...
   Click Troubleshoot.
   Click Advanced options.
   Select UEFI Firmware Settings.
   Click Restart.

Is there a separate bios access somewhere?

So what I gather is is that you have 1 card a R7 M260 which has a Controller by Intel and AMD Grahics software. At least is what I am thinking. Where did you get your AMD software drivers from AMD or from Toshiba ? Thinking that you need to only use drivers supplied by Toshiba in that update thing they have. I maye wrong on this but thinking it is more of a Toshiba issue than Firefox issue. Also Windows 10 installs driver updates and will over write your drivers with it's driver. Can find out in the Device Manager then vid card then Driver on the Properties Tab. On Windows 10 Pro can turn this off, on Windows 10 Home or others you can not and have to hack the registry. This could be the issue you are having/or not..... I have Pro and turned it off. This decribes how for both Pro & Home https://www.howtogeek.com/302595/how-to-stop-windows-10-from-automatically-updating-hardware-drivers/ Thinking still need more info to figure this out.

In the device manager, it shows them as 2 separate devices. But in the BIOS I can't even find a section showing any graphics options, let alone one that I can try to change.

As for the drivers, When I first found this issue I had not done anything special with the drivers. I tried to update the driver through the device manager letting it find it's own, and it updated the driver, though it was not using a Radeon driver. Restarted the computer and there had been no change in firefox. I then went to Toshiba's support page to download the driver through Toshiba, however there were no graphics drivers listed. So I went to Radeon's site to download the newest drivers (Which, iirc, were about a year and a half newer than the previous drivers date). Downloaded and installed the most up to date drivers. Restarted, and still no change in the settings within firefox.

I'm running Windows 10 Home

Within the Device Manager it is listing two display adapters 1: AMD Radeon R7 M260

 Driver Provider: Advanced Micro Devices, Inc.
 Driver Date: 6/12/2017
 Driver Version: 22.19.171.257

2. Intel(R) HD Graphics Family

 Driver Provider: Intel Corporation
 Driver Date: 11/10/2016
 Driver Version: 20.19.15.4549

In your Catalyst Control Center should be the option to switch the specific application to use AMD GPU.

Maybe these links will help you => http://en.community.dell.com/support-forums/laptop/f/3518/t/19474269 https://support.serato.com/hc/en-us/articles/202305784-Changing-graphics-card-settings-to-use-your-dedicated-GPU-on-a-Windows-computer-