Running Firefox 102.11.0esr on Debian 11 desktop

Firefox is very, very slow in responding to the cursor which doesn't show up as an arrow initially (as it normally would) - so if I point at Reply (for example), normally the cursor would be an arrow, the Reply box would turn yellow and I would click which would activate the command. At the moment there is no arrow, the Reply box stays grey and nothing happens if I click the mouse button. Eventually though after about two minutes the action is done. This is happening with any command in Firefox, e.g. trying to delete text in a draft message or trying to open an email in my inbox etc. etc. - all of it is the same as above and takes about two minutes to happen.