Menus not visible in some editions of firefox 
Author: Len K.Since the last (I think) update to V14 (v14.0.6.2) possibly earlier, and in v15 the full size menu bars on my websites no longer display in the version of Firefox on my development PC (v 59.0.2 (32-Bit)). when the screen size is reduced the tablet and mobile versions display the hamburger bar and menus correctly. I have not been too worried about this as the published websites have working menus on all other PCs which I have been able to check on. That is the problem is only with displays in Firefox on my PC, all other browsers work correctly.
It could be that this is a Firefox problem rather than a WebSite X5 problem, but somewhere there is an incompatibility.
Today I had a bigger problem with Website X5 itself which I have reported separately (text objects cannot be edited, preview not working), but I am now concerned that these problems could be in some way related as they both are in the area of display.
Len, is it possible to provide a link?
If you do not wish to overwrite the existing site, perhaps you could create a folder and upload the development site there?
We could then look eg www.mydomain.com/test
As for your other problem, have you recently restarted your PC? I have experienced this issue due to a pending windows 10 update.
Author
I only posted this because I have another, much more serious, problem with using X15 since 15.0.2 was installed (text objects, HTML objects do not display existing text in the edit window and do not have a cursor to input new text, does not display anything in the preview window), and I wondered if they were related.
The menu display problem is only visible in Firefox and ONLY on my PC! All other installations of Firefox on other PCs, and all other browsers on my PC work fine. As this has been a problem in X14 since November or earlier and in X15 (when it was working 15.0.1) I have and still assume it's a Firefox problem.
It's happening on more than one Website, a simple example is http://www.ensemble-paulinum.de/ on my PC (and I repeat only in Firefox) the menu bar on the left does not appear. If I narrow the display the hamburger bar and menu work fine. I expect it will all look fine if you try it!!
Len, your link comes up server not found I'm sorry
Author
Thank you all for the suggestions, Windows has just downloaded and automatic update (22. März 2018 – KB4089848) and after that was installed and restarted it looks like all the problems on my other installation have gone away.
@Esahc.. sorry, typo in the link, should have been http://www.ensemblepaulinum.de/ ; however, it's all working for me now, so the problem seems to have been Windows based as both this and the WebSite problem have been fixed by the Windows update. Both Firefox and WebSite had new installations recently because of new releases and it looks like new installations were suffering from some Windows installation error.
:-) - excellent!!