When browsing sites that use SELECT dropdowns, the dropdown box cannot be interacted with using the mouse. Using the keyboard to select a select box, then using the up / down arrow to change options works - but you cannot select / change the contents of the select box via the mouse.

This works fine if you start firefox with: GDK_BACKEND=x11 firefox

GPU is an AMD RX5700XT.

An example web site is:
https://www.ebay.com.au/itm/USB-Type-A-to-Mini-USB-90-Angle-Male-Plug-Adapter-Cable-M-M-Cord-Left-Right-AM/163915670633

 $  rpm -qa | grep firefox
firefox-70.0.1-4.fc31.x86_64

 $  rpm -qa | grep mesa | sort
mesa-dri-drivers-19.2.4-1.fc31.i686
mesa-dri-drivers-19.2.4-1.fc31.x86_64
mesa-filesystem-19.2.4-1.fc31.i686
mesa-filesystem-19.2.4-1.fc31.x86_64
mesa-libEGL-19.2.4-1.fc31.x86_64
mesa-libgbm-19.2.4-1.fc31.x86_64
mesa-libGL-19.2.4-1.fc31.i686
mesa-libGL-19.2.4-1.fc31.x86_64
mesa-libglapi-19.2.4-1.fc31.i686
mesa-libglapi-19.2.4-1.fc31.x86_64
mesa-libGLU-9.0.1-1.fc31.x86_64
mesa-libxatracker-19.2.4-1.fc31.x86_64
mesa-vdpau-drivers-19.2.4-1.fc31.x86_64
mesa-vulkan-drivers-19.2.4-1.fc31.i686
mesa-vulkan-drivers-19.2.4-1.fc31.x86_64

 $  rpm -qa | grep llvm | sort
llvm-libs-9.0.0-1.fc31.i686
llvm-libs-9.0.0-1.fc31.x86_64

 $  lspci | grep VGA
1e:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Navi 10 [Radeon RX 5700 / 5700 XT] (rev c1)

 $  dmesg | grep -i amdgpu
[    3.952520] [drm] amdgpu kernel modesetting enabled.
[    3.952647] amdgpu 0000:1e:00.0: remove_conflicting_pci_framebuffers: bar 0: 0xe0000000 -> 0xefffffff
[    3.952648] amdgpu 0000:1e:00.0: remove_conflicting_pci_framebuffers: bar 2: 0xf0000000 -> 0xf01fffff
[    3.952649] amdgpu 0000:1e:00.0: remove_conflicting_pci_framebuffers: bar 5: 0xfca00000 -> 0xfca7ffff
[    3.952651] fb0: switching to amdgpudrmfb from EFI VGA
[    3.952684] amdgpu 0000:1e:00.0: vgaarb: deactivate vga console
[    3.972884] amdgpu 0000:1e:00.0: No more image in the PCI ROM
[    3.972930] amdgpu 0000:1e:00.0: VRAM: 8176M 0x0000008000000000 - 0x00000081FEFFFFFF (8176M used)
[    3.972931] amdgpu 0000:1e:00.0: GART: 512M 0x0000000000000000 - 0x000000001FFFFFFF
[    3.973032] [drm] amdgpu: 8176M of VRAM memory ready
[    3.973034] [drm] amdgpu: 8176M of GTT memory ready.
[    4.588976] amdgpu: [powerplay] SMU is initialized successfully!
[    4.825139] fbcon: amdgpudrmfb (fb0) is primary device
[    4.825141] amdgpu 0000:1e:00.0: fb0: amdgpudrmfb frame buffer device
[    4.833050] amdgpu 0000:1e:00.0: ring 0(gfx_0.0.0) uses VM inv eng 4 on hub 0
[    4.833051] amdgpu 0000:1e:00.0: ring 1(gfx_0.1.0) uses VM inv eng 5 on hub 0
[    4.833052] amdgpu 0000:1e:00.0: ring 2(comp_1.0.0) uses VM inv eng 6 on hub 0
[    4.833052] amdgpu 0000:1e:00.0: ring 3(comp_1.1.0) uses VM inv eng 7 on hub 0
[    4.833053] amdgpu 0000:1e:00.0: ring 4(comp_1.2.0) uses VM inv eng 8 on hub 0
[    4.833054] amdgpu 0000:1e:00.0: ring 5(comp_1.3.0) uses VM inv eng 9 on hub 0
[    4.833054] amdgpu 0000:1e:00.0: ring 6(comp_1.0.1) uses VM inv eng 10 on hub 0
[    4.833055] amdgpu 0000:1e:00.0: ring 7(comp_1.1.1) uses VM inv eng 11 on hub 0
[    4.833056] amdgpu 0000:1e:00.0: ring 8(comp_1.2.1) uses VM inv eng 12 on hub 0
[    4.833056] amdgpu 0000:1e:00.0: ring 9(comp_1.3.1) uses VM inv eng 13 on hub 0
[    4.833057] amdgpu 0000:1e:00.0: ring 10(kiq_2.1.0) uses VM inv eng 14 on hub 0
[    4.833057] amdgpu 0000:1e:00.0: ring 11(sdma0) uses VM inv eng 15 on hub 0
[    4.833058] amdgpu 0000:1e:00.0: ring 12(sdma1) uses VM inv eng 16 on hub 0
[    4.833059] amdgpu 0000:1e:00.0: ring 13(vcn_dec) uses VM inv eng 4 on hub 1
[    4.833059] amdgpu 0000:1e:00.0: ring 14(vcn_enc0) uses VM inv eng 5 on hub 1
[    4.833060] amdgpu 0000:1e:00.0: ring 15(vcn_enc1) uses VM inv eng 6 on hub 1
[    4.833060] amdgpu 0000:1e:00.0: ring 16(vcn_jpeg) uses VM inv eng 7 on hub 1
[    4.833207] [drm] Initialized amdgpu 3.33.0 20150101 for 0000:1e:00.0 on minor 0