TB changes window size depending on message content (Linux)

[jcarretero]

I am using Ubuntu 16.04 LTS and Thunderbird 45.7.0 both with all the latest repository updates. I am using this on a laptop with a relatively small screen which means I am most often using Thunderbird with the window maximised. I use classic view with folder pane turned on.

In general all works fine except that every once in a while, mostly when I open e-mail messages from colleagues who use HTML encoding, the text instead of wrapping to the width of the current window it makes my window resize to the width of the text. This is extremely annoying as the window then grows beyond the width of my screen. This in turn means I can't really read the messages without having a portion of the text cropped (instead, I have to move the window so I can read).

Also, when one such message is being displayed, I cannot even maximise the window anymore or decrease the width. If I change to a different message then I have no problems resizing or maximising.

When I use Thunderbird on my desktop with a larger screen and therefore a larger Thunderbird window I do not see this behaviour. On my desktop I am running the same OS and Thunderbird versions as on the laptop.

I do not see why Thunderbird is given permission to resize the window.

This has been going on for quite a while now. But finally today decided to ask to see if someone else may have experienced this behaviour and found a solution.