It could be caused by any of those things, or your anti virus or some other security software.

I would start by checking your add-ons to make sure the one that reduces sizes is actually still enabled.

Hi Matt, and thanks for your input. I have tried the following to no avail:- 1. Check of all Thunderbird Account and Option settings - all reconfirmed except that I also approved Pop-ups (previously prohibited); 2. Ditto Firefox. No changes. 3. Looked at my add-ons - only LastPass - so I remvoed it and reinstalled same. No correction of problem. 4. Looked at my AV product (Avast) settings and all seemed to be valid and/or not of likely impact on problem; 5. Uninstalled Thunderbird r38.0.1 (Control Panel > Add/Remove Programs), downloaded afresh and installed r 38.0.1. All settings appear to have been retained. 6. Retested my problem (loss of jpg dialogue) which has not been affected and is still missing after all of the above. Your next suggestion will be welcome. If I look at my Control Panel > Add/Remove Programs options for Windows components, I see I could try uninstalling Internet Explorer. I wonder if this might assist followed by a reinstall, however I am not confident that my CDs would allow component re-install. My XP SP3 install CD starts off down the path of a full install, although it might be possible to break into a Recovery Console and possibly selective re-install approach (Press "R" while proceeding?). Any and all ideas welcome. Geoff.

Hmm, the actions for adjusting picture size in Thunderbird all work at the point of sending, that is, after the message has been composed. The process you describe seems to take place before the email client is even opened, so I suspect your problem and its solution life in the Windows shell.

There is a relationship between Windows Explorer and Internet Explorer, to the extent that it is, or has been, possible to surf the Web from Windows Explorer. However I don't expect that twiddling with IE will do anything useful for broken shell issues.