I still have this problem.

re :I don't know how I ended up with double spacing. Perhaps you have the option to 'Use paragraph format...' selected.

Menu app icon > Options select 'Composition' Under 'HTML Style' uncheck checkbox 'Use Paragraph format instead of Body Text by default'

See image below as guide.

It is also possible you have selected to use a font that looks like it is bold. That could have been set in the same area as mentioned above. Note: Under 'HTML Style', I have the setting 'Font: Variable width' I suggest you check that setting at the same time.

The double spacing was fixed, but I am unable to turn on or off the Bold. I can live with the bold because it is easier to read. I checked the varying length under html, but I don't see anything that helps.

Version 78.6.1 The above, previously submitted, answers did not work for me regarding double space after pressing the Enter key while typing. Very frustrating. What I found that DID solve the problem at least to the point where I could muddle through completing my work and not type a ridiculous looking email while entering some names and addresses in response to an inquiry was to press the Shift key while pressing Enter. I got a standard, single-spaced new line that way. It continued to give me a double-space when just pressing Enter, symbolizing a new paragraph. I tried every combination of Ctrl Enter, Alt Enter, and finally Shift Enter and it worked. Lots of lost time.

wn3i The above works, but not in any write window that was open at the time of changing the setting as that pre-opened window would still have the old paragraph formatting. A new Write window should work as expected providing it does not contain any formatting that would control that email.

Please note: there are a few other occasions when it might fail. eg: If you are 'Replying' to an email When you click on 'Reply' the entire contents of the original email from sender is copied into a new 'Write' window ready for you to enter your comment. The entire contents includes any formatting the sender included in the original email. So if the sender included html css that specifically sets a paragraph to be double space, then it will control the comments you are adding.

eg: used a template email that was created with paragraph formatting set as double space or used an email as 'Edit as new message' which contained html css that controls the formatting in that email.

It is a real nuisance when people include a load of formatting that tries to control certain aspects of their emails. There is often an issue when people copy paste from other programs such as MSWord which may contain aload of formatting. Sometimes people do not even realise what is really in their emails.

If the setting was ok until you restarted Thunderbird, then you need to check if you have 'cleanup' software that was deleting the session, cache, cookie etc files in Thunderbird. Such programs as 'CCleaner' or even some Anti-virus products offer cleaning up of files. If you intend to keep using those types of programs then you need to make sure the Thunderbird profile folders are exempt.

The information you posted to use 'Shift + Enter' may be of help to some people or help if effected when using a 'Reply' and the original sender included a load of css in email.

Yes that problem is frustrating. I don't have that problem with all of my emails. I did make the adjustment above using the 'chosen solution' which helped with most of my replies.

What I did in the problem emails, in order to keep the thread information intact in my reply, was to 'copy' the entire thread (just takes a sec.),click reply and paste it OVER THE TOP of everything in the reply before I started typing.

I don't know why but it worked for me.