It could be the work of one of your add-ons, or it could be Hardware Acceleration. How to disable Hardware Acceleration {web link}

Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All Of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is, detective.

In the address bar, type about:crashes<enter>. Note: If any reports do not have BP- in front of the numbers/letters, click it to submit them.

The crash report is several pages of data. We need the report numbers to see the whole report.

Using your mouse, mark the most recent 7 - 10 Submitted crash reports, and copy them. Now go to the reply box and paste them in.

For more help on crash reports, see; https://support.mozilla.org/en-US/kb/firefox-crashes-asking-support

for example this is a report number

099e1f32-d514-4484-a5ac-4dd0f0190910

bp-099e1f32-d514-4484-a5ac-4dd0f0190910 Signature: asepkcs.dll | patched_BaseThreadInitThunk

Crash Reason EXCEPTION_PRIV_INSTRUCTION

aswamsi.dll = Avast

asepkcs.dll = Athena Smartcard Solutions

Update your Avast. If the problem continues, disable it.

i think it's ok! thank youuuu

Glad to help. Safe Surfing.