@Tha_Bozz : I'm never getting my toolbar icon customisation changed here between updates
Go to Menu -> Settings -> Permissions and Data then check "Allow Firefox to run feature studies" is off.
That feature allows random-settings changes to be made with selected users only to test things.
Also in the Settings, click the "Firefox Labs" category and see if you've opted-into anything there that
might reset toolbar layouts.
Lastly, type about:policies into the URL bar, then press ENTER.
If you see "The Enterprise Policies service is inactive", this is normal on a home / personally-owned PC.
If you're using a company-issued device, it may list policies your company has set.
One of those may be the toolbar layout reverting to how they've set it each close / re-open of Firefox.
