"Corrupted Content Error" Gmail blocker ransomware

I use a laptop running Linux and suddenly became unable to access gmail; a screen appeared with a "Corrupted Content Error" message. Then I got a telephone call from someone with an Indian accent who said he was from BT and I had a fault in my  laptop (I don't use BT) who wanted me to enter a code, but his speech was too indistinct. I am not expert enough to solve this, has anyone managed to deal with the same problem?

Hi JH_Atkinson:

Try clearing your Firefox browser cache and delete your saved cookies as suggested in the Firefox thread Corrupted Content Error When Opening GMail.  I'm not sure about the Linux version of Firefox, but in my FF ESR browser I can go to History | Clear Recent History, select Everything for a time range and clear all items in my history.

...Then I got a telephone call from someone with an Indian accent who said he was from BT and I had a fault in my  laptop (I don't use BT) who wanted me to enter a code, but his speech was too indistinct.

That sounds like a scam technical support phone call - I'd advise that you simply hang up on them if they call back.  It could be a coincidence that you got this phone call around the same time you started having problems with GMail but it might be prudent to run a full system scan for malware with your antivirus just in case you visited an malicious web site that installed something more serious than a tracking cookie (e.g., like a browser hijacker) in your browser.

If you had a Windows OS I would normally suggest a second-opinion on-demand scan with Malwarebytes in addition to a full system scan with your antivirus but I checked the Malwarebytes website and it doesn't appear they have developed a Linux-compatible scanner yet.
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32-bit Vista Home Premium SP2 * Firefox ESR v52.9.0 * Norton Security v22.15.1.8